Report on the Radiolaria/Discoidea

by Ernst Haeckel

Suborder V. DISCOIDEA, Haeckel (Pls. 31-38, 41-48).

Discida vel Discoidea, Haeckel, 1862, Monogr. d. Radiol., pp. 56, 476.
Discoida, Discoidea, Discida, Haeckel, 1878, Protistenreich, p. 103.

Definition.—Spumellaria with discoidal or lenticular central capsule (often with radial prolongations, rarely allomorphic); with discoidal or lenticular fenestrated siliceous shell (often with radial spines or fenestrated arms, rarely allomorphic). Growth reduced or diminished in the direction of one dimensive axis.

The section Discoidea comprises those Spumellaria in which the fenestrated shell is more or less discoidal or lenticular, flattened or compressed in the direction of one axis. The geometric fundamental form of the latticed shell, which in the Sphæroidea is a sphere, here becomes a flat disk, like a medal, or a biconvex lens, sometimes also a biconcave lens. The Discoidea can be derived from the Sphæroidea by shortening of one axis. This shortened vertical axis is the main axis of the disk; both its poles are constantly equal. Perpendicular to this axis is the equatorial plane of the disk by which it becomes divided into equal halves. In the simplest forms of Discoidea all axes of this horizontal equatorial plane (all "equatorial axes" or "cross axes") are equal; in the most of the genera and species these cross axes are different, so that rays of stronger growth ("perradii") alternate with rays of weaker growth ("interradii"). The number of these cross axes distinguishable is commonly two to four, rarely more. In the direction of these are developed either radial marginal spines or spongy arms.

The order Discoidea was founded in my Monograph (1862, p. 476) as the family "Discida" (Radiolaria with flat discoidal or biconvex lenticular shell), comprising the "Calodictya and Lithocyclidina" of Ehrenberg and a great part of his "Haliommatina." As three different subfamilies of that family I separated the Coccodiscida (with five genera), the Trematodiscida (with seven genera), and the Discospirida (with two genera; Monogr. d. Radiol., p. 485). A fourth group of Discoidea was constituted by the Spongodiscida (with eight genera, including the Spongocyclida), which at that time I united with the Spongurida, because of their spongy structure (loc. cit., p. 452).

As the number of fossil Discoidea found in the Tertiary rocks of Barbados and of the Mediterranean shores (Sicily and Greece) is comparatively very large, we find even in the first system of Polycystina of Ehrenberg (1847), not less than twelve genera distinguished, viz., six Calodictya, two Haliommatina, and four Lithocyclidina (Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1847, p. 53). The whole number of Radiolarian genera distinguished in that first system was forty-four. The diagnoses of them given by Ehrenberg were as usual very insufficient. The characters of the three families given by him were the following:—Calodictya—"Testarum intus spongiosarum et nucleo destitutarum orbes; Haliommatina—Testæ subglobosæ nucleus radiatus; Lithocyclidina—Testarum disci in media parte nucleati margine celluloso." In the latest work of Ehrenberg (1875, p. 157) the same system was repeated, but some new genera added; and thirty-eight different species, appertaining to the Discoidea, were figured in the same work (Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Tafs. xx.-xxx.).

Richard Hertwig, 1879, in his excellent work, Der Organismus der Radiolarien (pp. 57-68), gave a detailed description of the skeleton of some Discoidea, and arrived at the conclusion that this whole family had a spirally constructed skeleton, and should therefore be derived from the Lithelida. But this conclusion is certainly erroneous, and in my opinion the whole explanation of that spiral structure, and of its signification in the development of Discoidea, is the weakest part of that otherwise very important work.

In my Prodromus (1881, p. 456) I gave a provisional system of the Discida or Discoidea from the immense quantity of new material collected by the Challenger, and could distinguish not less than eighty-four genera. This number is from subsequent research only augmented by seven, so that in the following pages ninety-one genera with five hundred and one species are described. In the Prodromus I had disposed them in four different families, which number is now increased to six. These six families can be again disposed in two main groups or sections, the Phacodiscaria and the Cyclodiscaria, each section with three families.

The Phacodiscaria are characterised by the possession of a typical "phacoid shell," and contain the three families Cenodiscida, Phacodiscida, and Coccodiscida. On the other hand, the Cyclodiscaria are distinguished by the absence of such a "phacoid shell," and contain the three families Porodiscida, Pylodiscida, and Spongodiscida. Both sections exhibit an analogous development.

The Cenodiscida (Pl. 48, figs. 1-3) open the series of the Discoidea as their simplest forms; a discoidal or lenticular simple lattice-shell encloses a central capsule of the same form, and is separated from it by the calymma or jelly-veil. The common ancestral form of this family is Cenodiscus, without radial marginal spines; it can be derived from Cenosphæra in the most simple way, by flattening in one axis. If on the equatorial margin of the lens a peculiar solid girdle be developed, we obtain Zonodiscus; in all other genera of the Cenodiscida radial spines are developed on the margin. As the simple lenticular cortical shell of Cenodiscus, in which the central capsule is enclosed, is most characteristic not only of this family, but also of the two following families, we call it the phacoid shell (that is, a lenticular extracapsular or cortical lattice-shell).

The Phacodiscida (Pls. 31-35), the second family, have the same extracapsular "phacoid shell" as the Cenodiscida, but differ from these by the possession of one or two intracapsular concentric medullary shells, which are connected with the former by radial beams, perforating the lenticular central capsule. The radial beams are commonly numerous, and arranged in two opposite bunches around the shortened main axis. But often also besides these occur other longer radial beams, situated in the equatorial plane; the number of these is commonly four, and they form a regular rectangular cross, lying opposite in pairs in two equatorial diameters, perpendicular one to another. In the simplest genera of this family (the Sethodiscida) the equatorial margin of the phacoid shell is simple or surrounded by a solid smooth girdle; in all other genera are developed on the margin solid radial spines lying in the equatorial plane, either regularly disposed in a somewhat constant number (two to eight, Heliosestrida), or irregularly disposed, in a larger and more variable number (ten to twenty or more, Heliodiscida).

The Coccodiscida (Pls. 36-38) form a third family of the Discoidea, directly associated with the Phacodiscida; both have the same characteristic extracapsular "phacoid shell," which is connected by radial beams with a simple or double, intracapsular medullary shell. But whilst in the foregoing family the equatorial margin of the phacoid shell is simple or only armed with radial spines, in the Coccodiscida it is surrounded by peculiar concentric chambered girdles, or rings, which resemble those of the following family, the Porodiscida. Each of these "chambered girdles" is composed of a circular ring in the equatorial plane, a variable number of radial beams dividing it into incomplete chambers, and two porous cover-plates or "sieve-plates," covering the upper and lower face of the disk. These sieve-plates may be regarded as incomplete lenticular cortical shells, which are only developed in the peripheral part of the disk, whilst their central part is represented by the only complete cortical shell, the "phacoid shell." The number of these concentric chamber-girdles amounts to from one to ten or more. The margin of the disk is either simple (Lithocyclida) or armed with radial spines (Stylocyclida), or provided with two to five chambered radial arms (Astracturida); the structure of the arms is the same as that of the girdles.

The Porodiscida (Pls. 41-47), the largest family of all Discoidea, begins the series of Cyclodiscaria, or those Discoidea in which there is no "phacoid shell," but a small simple central chamber surrounded by a number of small latticed chambers of nearly the same size and form. In the Porodiscida these chambers are arranged in complete circular concentric rings or spiral convolutions; in the small family of Pylodiscida the central chamber is surrounded by three radial arm-chambers separated by three open spaces; in the third family of Cyclodiscaria, the Spongodiscida, all the chambers are arranged more or less irregularly, and the whole disk becomes spongy; also the surface of the disk is spongy, whilst in both former families it is covered by two regular even porous plates or "sieve-plates." Probably all Cyclodiscaria can be derived phylogenetically from Archidiscus, a very small and simple lenticular disk, which is composed of a small spherical latticed central chamber and of a single concentric chambered ring or girdle; the margin of this ring is connected with the central chamber by a variable number of radial beams. This Archidiscus can be derived either from Saturnalis (Pl. 13, fig. 16.) by the development of lattice-work between the equatorial ring and both polar faces of the concentric central chamber, or from Sethodiscus (Pl. 33, figs. 1-3) by flattening of the lenticular shell, so that the enclosed inner medullary shell (the central chamber) meets the outer phacoid shell at both poles.

The Porodiscida are commonly flat or biconvex (rarely biconcave) disks, the central chamber of which is surrounded not by a single, but by a variable number (commonly three to six) of concentric chambered girdles or rings; they arise from Archidiscus by apposition of new concentric chambered rings around the first ring, all lying in the equatorial plane. Afterwards the disk often becomes thickened by apposition of concentric chamber-rings on both flat sides also, so that two to four or more layers are stratified one over the other. The circular concentric rings often become interrupted, or spirally convoluted (wholly or partially); also the chambers sometimes become irregularly crowded. But in all cases both surfaces of the disk (upper and lower) continue to be porous plates or sieve-plates, at least in the centre, but they never become spongy.

The margin of the disk exhibits in the Porodiscida a great variety of different forms, serving for distinction of subfamilies and of genera. In the Trematodiscida the margin remains quite simple, as in the Archidiscida, or is only surrounded by a hyaline equatorial girdle. In the Ommatodiscida it is distinguished by one or two peculiar oscula, surrounded by a corona of spines. The Stylodictyida are distinguished by a number of solid radial spines, and the Euchitonida by a number of chambered, or spongy, radial arms, arising from the margin of the disk and lying in the equatorial plane. The variety of these radial marginal appendages is in the Porodiscida much greater than in the Coccodiscida.

The Pylodiscida (Pl. 48, figs. 12-20) represent a new, small, but very remarkable family of Discoidea, all triradial, and distinguished by the peculiar formation of large open spaces in the latticed discoidal shell, which reappear in a similar shape among the Larcoidea in the Pylonida (Tetrapyle, &c.). We get the best understanding of this peculiar formation if we return to Archidiscus, probably the common ancestral form of all Cyclodiscaria, of the Porodiscida as well as of the Pylodiscida and Spongodiscida. In some species of Archidiscus (Archidiscus hexoniscus, Archidiscus pyloniscus, &c.) the small lenticular shell is composed of a spherical latticed central chamber and of a concentric equatorial girdle composed of six such chambers, either all six equal, or alternately larger and smaller. This latter form is nearly identical with Triodiscus, and if we imagine the lattice-work of only three ring-chambers complete, whilst that of the three alternating chambers is reduced to the marginal ring, we get Triopyle, by loss of this ring Triolene (a disk composed of four simple lattice-chambers, lying in one plane, three radial around one central spherule). The genera mentioned form together the subfamily of Triopylida. In the second subfamily, Hexapylida, the same formation is doubled; here three double arm-chambers are separated by three double spaces (two in each radius). Also here the three distal spaces may be either quite open (Pylolena), or half closed by the marginal girdle (Hexapyle), or quite loosely latticed (Pylodiscus). If the margin of this latter form become surrounded by a perfect chambered equatorial girdle, we get Discozonium, and if this acquire a peculiar marginal ostium (surrounded by a corona of spines) we arrive at Discopyle. These two latter genera form the third subfamily, the Discopylida. The eight genera of Pylodiscida represent therefore a continuous phylogenetic series.

The Spongodiscida are the sixth and last family of the Discoidea, differing from the five other families in the irregular, spongy structure of the discoidal skeleton; both surfaces of the flat disk (upper and lower) are here principally covered with a rough, spongy framework, whilst in the five other families they are covered by the flat and smooth porous plates or sieve-plates. Nevertheless there is no sharp boundary between the Spongodiscida and the closely allied Porodiscida. In these latter also the discoidal shell becomes often more or less spongy (mainly in the peripheral part, e.g., in Myelastrum, Pl. 47); but at least the central part of the disk here remains constantly covered by sieve-plates. The massive skeleton of the Spongodiscida is either of perfectly irregular structure, only composed of innumerable fine branched siliceous threads, interwoven in all possible directions; or only the outer part of the disk is composed of such spongy framework, whilst the central part is more or less distinctly composed of concentric chambered rings, as in the Porodiscida. These latter forms indeed exhibit an immediate transition to this family, and were formerly (in 1862) separated by me as Spongocyclida. Also the polymorphous shape of the disk margin in the Spongodiscida is quite analogous to that of the Porodiscida. Whilst in the first subfamily, the Spongophacida, the margin is quite simple; in the second, the Spongotrochida, it is armed with solid radial spines; and in the third, the Spongobrachida, it is provided with two, three, or four spongy, radial arms—the former as well as the latter lying in the equatorial plane of the disk, either regularly or irregularly disposed.

The Equatorial Margin of the lenticular disk exhibits in all six families of Discoidea similar characters, mainly serving for the distinction of subfamilies and genera. In the most primitive genera of all six families the margin is simple, without radial prolongations (spines or arms); it is quite simple in Cenodiscus, Sethodiscus, Phacodiscus, Lithocyclia, Coccodiscus, Archidiscus, Porodiscus, Pylodiscus, and Spongodiscus. In some genera the simple margin of the lenticular disk is bordered and surrounded by a thin, hyaline, equatorial girdle of silex, either quite solid or slightly porous (Zonodiscus, Periphæna, Perizona, Perichlamydium, and Spongophacus).

A quite peculiar and remarkable character of few genera is the development of one or two oscula, larger marginal openings, which are surrounded by a corona of spines, and probable are fit for the issue a peculiar bunch of pseudopodia or of a "sarcode flagellum." Such oscula occur only in two families of Cyclodiscaria; in the Porodiscida and Pylodiscida; in the former Ommatodiscus, in the latter Discopyle (Pl. 48, figs. 19, 20) is distinguished by a single marginal osculum; besides this, in the former occurs Stomatodiscus, with two such oscula, opposite on the poles of one axis (Pl. 48, fig. 8). These oscula may be compared with the similar polar formations in some Ellipsida (Lithomespilus) and in many Cyrtoidea; but they do not prove a nearer affinity with the latter, and are only analogous, not homologous.

Radial Spines occur on the margin in the equatorial plane of the Discoidea in the greatest variety of number, form, size, and disposition. If the number be low (between two and eight) they are commonly regularly disposed; if the number be larger (ten to twenty or more) their disposition becomes commonly more or less irregular. The regular disposition is of great promorphological importance, as indicating the axes in which the growth is preponderant, and introduces other peculiar radial formations. Regarding these axes we can generally distinguish two groups, Artiacantha with a paired number (two, four, eight), and Perissacantha with odd numbers (usually three). The section of Artiacantha could be divided into three following groups:—A. Stylodiscida, with two radial spines only, lying opposite on both poles of one equatorial axis (the "first cross axis")—Stylodiscus, Sethostylus, Stylocyclia, Xiphodictya, Spongolonche (Pl. 31, figs. 9-12; Pl. 38, fig. 1; Pl. 42, figs. 10-12, &c.); B. Staurodiscida, with four radial spines, lying opposite in pairs on the poles of two crossed equatorial axes, perpendicular to one another (first and second cross axes)—Crucidiscus, Sethostaurus, Staurocyclia, Staurodictya, Spongostaurus (Pl. 31, figs. 1-8; Pl. 37, figs. 1-4; Pl. 42, figs. 1-6; Pl. 48, fig. 2, &c.); C. Octostylida, with eight radial spines, opposite in pairs in four axes, which are crossed at angles of 45°—Heliosestrum, Astrosestrum, &c. (Pl. 32, figs. 4, 5; Pl. 34, figs. 3, 6); in this latter case sometimes the radial symmetry is the same as in many Medusæ, four larger (perradial) spines alternating with four smaller (interradial), indicating radii of first and second order. The section of Perissacantha is much smaller, and commonly represented only by triradial forms, with three spines at equal distances (120°)—Triactis, Tripocyclia, Tripodictya, Spongotripus, &c. (Pl. 33, fig. 6; Pl. 37, fig. 5; Pl. 42, figs. 7-9).

Radial Arms on the margin of the disk appear in similar variety of number, form, and disposition as the radial spines; but the number is here commonly limited to from two to four, rarely five to six. The arms are absent in the families Cenodiscida and Phacodiscida; in the four other families they return under similar forms. These arms are direct prolongations of the disk, and exhibit the same structure, so that they may be regarded both as centrifugal productions of certain radii, and also inversely as peripheral parts of a disk, the interjacent radii of which are reduced. The regular disposition and shape of the arms, an important character for the distinction of genera and species, is repeated in a quite analogous manner in the four above mentioned families, so that we can distinguish the following groups—A. Amphibrachida, with two radial arms, opposite on the poles of one equatorial axis (the first cross axis)—Diplactura, Amphibrachium, Spongobrachium (Pl. 38, figs. 3-5; Pl. 44, figs. 6-11); B. Triobrachida, with three radial arms; the most important group (with all Pylodiscida); either all three arms are equal and disposed at equal distances (Trigonactura, Dictyastrum, Rhopalodictyum, Pl. 38, figs. 6-9; Pl. 43, figs. 5, 13, 16; Pl. 48, figs. 12-19), or a single odd arm differs in size and position, and is often larger than both the opposite paired arms (Rhopalastrum, Euchitonia, Pl. 43, figs. 6, 10, 15, &c.); C. Tetrabrachida, with four radial arms, opposite in pairs in two crossed axes, commonly perpendicular one to another, Stauractura, Stauralastrum, Spongaster, &c. (Pls. 46, 47).

The arms are commonly simple, undivided, but sometimes also forked or branched (Pl. 43, figs. 15, 16; Pl. 47). Their basal parts are either free, separately inserted into the margin of the circular central disk, or they are connected by a "patagium," a peculiar connecticulum, like a web-membrane, which is composed of a chambered, commonly more or less spongy framework, different in texture from the lattice-work of the arms (Pl. 38, figs. 8, 9; Pl. 43, figs. 9-16; Pl. 46). Sometimes the patagium overgrows the whole shell. A peculiar modification of it appears in Stephanastrum (Pl. 44, fig. 1), where only the distal parts of the arms are connected by the ring-shaped patagium, whilst the basal parts are free; therefore open gates rest between them, like those of the Pylodiscida (Pl. 48, figs. 12-20).

The Central Capsule of the Discoidea is constantly discoidal, more or less lenticular; in some cases more biconvex, with vaulted faces and thin margin; in others more medal-shaped, with flat faces and thick margin. In the Cenodiscida alone the capsule lies freely inside the simple phacoid shell, and is separated from it by the jelly-veil. In the other five families the capsule encloses the central parts of the skeleton, and is enveloped by the superficial parts of it, whilst its membrane is perforated by radial beams connecting the latter with the former. In the Phacodiscida and Coccodiscida the capsule encloses the simple or double medullary shell, but is itself enclosed by the cortical phacoid shell. In all Cyclodiscaria (in the Porodiscida, Pylodiscida, and Spongodiscida) the capsule fills out the greatest part of the chambered or spongy skeleton, and is only protected by the superficial parts of it, in the Porodiscida and Pylodiscida by the covering sieve-plates, in the Spongodiscida by the spongy cortical substance of the shell. The growth of the capsule corresponds to that of the including shell, gradually increasing on the margin in the equatorial plane. Whilst in the greater number of Discoidea its form continues circular, in many forms provided with radial arms it enters into the arms and assumes their form. The protoplasm of the capsule is commonly coloured by brown or red pigment, and often contains many oil-globules. The nucleus is originally enclosed by the medullary shell or the central chamber, and with increasing size enters into the surrounding parts; in the Cyclodiscaria it often fills out the internal concentric rings. The extracapsular jelly or the calymma is commonly thick, and envelops the greater part or the whole body.

Synopsis of the Families of the Discoidea.

I. Section Phacodiscaria. Discoidea with external phacoid shell (or lenticular latticed cortical shell).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Phacoid shell simple, without enclosed medullary shell,			1. Cenodiscida.
		Phacoid shell with simple or double enclosed medullary shell.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Margin without chambered girdles,	2. Phacodiscida.
				Margin surrounded by by chambered girdles.	3. Coccodiscida.
II. Section Cyclodiscaria. Discoidea without external phacoid shell (no lenticular latticed cortical shell).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Surface of the shell covered by convex or even porous sieve-plates (not spongy).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Concentric rings around the central chamber complete without open spaces),	4. Porodiscida.
				Concentric rings around the central chamber interrupted by three open spaces,	5. Pylodiscida.
		Surface of the shell spongy, not covered by peculiar porous sieve-plates,			6. Spongodiscida.

Family XVIII. Cenodiscida, n. fam. (Pl. 31, fig. 11; Pl. 48, figs. 1-3).

Definition.—Discoidea with simple extracapsular phacoid shell (or lenticular latticed cortical shell), without medullary shell and without chambered equatorial girdles.

The new family Cenodiscida opens the long series Discoidea, as their most simple and primitive form. The circular lenticular central capsule is enclosed by a simple latticed shell of the same form, only separated from it by a thinner or thicker jelly-veil. The lenticular or discoidal fenestrated shell is therefore an extracapsular or "cortical shell," without an enclosed medullary shell.

The few genera of the Cenodiscida differ only in the shape of the equatorial margin of the lenticular disk. In the first subfamily, Zonodiscida, the margin is either quite simple (Cenodiscus) or surrounded by a smooth, solid equatorial girdle (Zonodiscus). In the second subfamily, Trochodiscida, the margin is armed with solid radial spines, lying in the equatorial plane. According to the number and disposition of these marginal spines, we distinguish Stylodiscus (with two spines, opposite in one equatorial axis), Crucidiscus (with four spines, opposite in pairs in two equatorial axes, perpendicular one to another), Theodiscus (with three marginal spines), and Trochodiscus (with numerous, commonly twenty to thirty, irregularly disposed spines). The spines are constantly simple, not branched; sometimes more conical or cylindrical, at other times more angular or pyramidal.

The two convex faces of the lenticular shell are constantly of similar shape, commonly smooth, sometimes more or less thorny, or armed with bristle-shaped radial spines. The pores are commonly more or less regular, circular, and disposed in series, which are occasionally more radial, at other times more concentric. If the wall of the hollow lens be rather thick, the difference in the shape of the central and peripheral pores is often striking. The central pores perforating the thick wall perpendicularly are short cylindrical tubes; the marginal pores perforating it in an oblique direction are longer conical tubes. The bars between the central pores are often somewhat smaller.

The Central Capsule of the Cenodiscida is in all cases a perfect, circular, biconvex lens, the equatorial diameter of which is commonly between two-thirds and three-fourths of the enclosing lattice-shell. The interval between the two is filled up by the jelly-veil, or the hyaline "calymma," which is perforated by the numerous pseudopodia that pass through the shell-pores.

As the Cenodiscida possess the most simple shell-form of all Discoidea, we may regard Cenodiscus as the common ancestral form of this large section, in the same manner as Cenosphæra is the ancestral form of Sphæroidea, Cenellipsis of the Prunoidea, Cenolarcus of the Larcoidea. But it is also possible that a part of Cenodiscida (or all?) arises from the Phacodiscida by reduction and loss of the medullary shell. For in some cases we find arising from the inside of the shell centripetal radial beams, which end at a certain equal distance from the hollow centre (Pl. 31, fig. 11; Pl. 38, fig. 2). Cenodiscus itself can be derived either from Cenosphæra by compression of the spheroidal shell in one axis, or from Sethodiscus by loss of the intracapsular medullary shell, or from Actidiscus (the lenticular Actissa) by formation of a cortical shell around the lenticular central capsule.

Synopsis of the Genera of the Cenodiscida.

I. Subfamily Zonodiscida. Margin of the disk without radial spines.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Margin quite simple, without equatorial girdle,	175. Cenodiscus.
		Margin surrounded by a solid siliceous equatorial girdle,	176. Zonodiscus.
II. Subfamily Trochodiscida. Margin of the disk armed with radial spines (lying in the equatorial plane).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Two spines opposite in one equatorial axis,	177. Stylodiscus.
		Three spines on the margin of the disk,	178. Theodiscus.
		Four spines opposite in pairs in two perpendicularly crossed equatorial axes,	179. Crucidiscus.
		Ten to twenty or more radial spines (variable in number and commonly irregular in disposition),	180. Trochodiscus.

Subfamily 1. Zonodiscida, Haeckel.

Definition.—Cenodiscida without radial spines on the margin of the disk.

Genus 175. Cenodiscus,^[1] n. gen.

Definition.—Cenodiscida with simple margin of the circular disk, without surrounding equatorial girdle and without radial spines.

The genus Cenodiscus is the most simple and primitive form of all Discoidea, and represents possibly the common ancestral form of this order. The latticed shell is a simple biconvex lens, and encloses a smaller central capsule of the same form, separated from it by the jelly-veil. Cenodiscus can be derived phylogenetically either from Cenosphæra by lenticular flattening of a simple latticed sphere, or directly from Actissa by formation of a lenticular fenestrated shell around the lentiform central capsule. Possibly also some forms of Cenodiscus can be derived from Sethodiscus by reduction and loss of the medullary shell.

1. Cenodiscus phacoides, n. sp. (Pl. 48, figs. 1, 1a).

Disk with smooth surface, without radial ribs or spines. Margin of the lenticular biconvex disk thin, simple. Pores regular, circular; fifteen to sixteen on the radius of the disk. (Very similar to Sethodiscus phacoides, but without medullary shell.)

Dimensions.—Diameter of the disk 0.2, of the pores 0.005.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

2. Cenodiscus rotula, n. sp.

Disk with smooth surface, without medial ribs or spines. Margin of the disk blunt, very thick, rounded; both faces little convex. Pores regular, circular; thirteen to fourteen on the radius of the disk. (Similar to Phacodiscus rotula, Pl. 35, fig. 7, but without medullary shell.)

Dimensions.—Diameter of the disk 0.16, of the pores 0.006.

Habitat.—North Pacific, Station 241, depth 2300 fathoms.

3. Cenodiscus lenticula, n. sp.

Disk with thorny surface, scattered with small, conical spines. Margin of the lenticular biconvex disk thin. Pores irregular, roundish; ten to eleven on the radius of the disk.

Dimensions.—Diameter of the disk 0.15, of the pores 0.008.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

Genus 176. Zonodiscus,^[2] n. gen.

Definition.—Cenodiscida with surrounding solid equatorial girdle on the margin of the lenticular disk, without radial spines.

The genus Zonodiscus differs from the preceding Cenodiscus only in the development of a solid siliceous girdle around the keen margin of the lenticular disk. This form can also be derived from Periphæna or Perizona by reduction and loss of the medullary shell. The same girdle formation returns not only in both these Phacodiscida (Pl. 32, fig. 7; Pl. 33, fig. 4), but also in the Porodiscid Perichlamydium.

1. Zonodiscus saturnalis, n. sp.

Disk with smooth surface, without radial spines. Pores regular, circular, fifteen to sixteen on the radius of the disk, in its distal half arranged in fifty to sixty radial series, which are separated by prominent radial crests or ribs. The crests are prolonged into the proximal half of the thin solid equatorial girdle, which is one-third as broad as the radius of the disk.

Dimensions.—Diameter of the disk 0.25, of the pores 0.05.

Habitat.—South Atlantic, Station 335, depth 1425 fathoms.

Subfamily 2. Trochodiscida, Haeckel.

Definition.—Cenodiscida with radial spines on the margin of the disk, disposed in the equatorial plane.

Genus 177. Stylodiscus,^[3] n. gen.

Definition.—Cenodiscida with two radial spines on the margin of the disk, opposite in one equatorial axis.

The genus Stylodiscus opens the series of the Trochodiscida or of those Cenodiscida in which the thin margin of the hollow lenticular disk is armed with a number of solid radial spines, situated in its equatorial plane. Stylodiscus is at the same time the most simple form of the Stylodiscida, or of the numerous Discoidea (belonging to different families) in which the disk bears only two spines, opposite in one equatorial axis. Hitherto only two species of this genus have been observed, but they seem to represent two different subgenera.

Subgenus 1. Stylentodiscus, Haeckel.

Definition.—Internal cavity of the shell with centripetal axial rods.

1. Stylodiscus endostylus, n. sp. (Pl. 31, fig. 11).

Sethostylus endostylus, Haeckel, 1881, Prodromus et Atlas (pl. xxxi, fig. 11).

Disk with smooth surface and dentated margin. Pores irregular, roundish; ten to twelve on the radius of the disk. Marginal teeth conical, short, irregular. Both opposite polar spines cylindrical, longer than the diameter of the disk, and as broad as one larger pore. On the inside of the hollow disk both spines are prolonged into two strong centripetal axial rods, which do not reach the centre. Also a number of smaller centripetal axial rods surrounds the central cavity, so that an original medullary shell (Sethostylus) seems to have been lost (comp. above, p. 410).

Dimensions.—Diameter of the disk 0.25, of the pores 0.005 to 0.02; length of the polar spines 0.3 and more, thickness 0.012.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Subgenus 2. Stylexodiscus, Haeckel.

Definition.—Internal cavity of the shell without axial rods.

2. Stylodiscus amphistylus, n. sp.

Disk with smooth surface and smooth margin. Pores regular, circular; eight to nine on the radius of the disk. Both opposite polar spines pyramidal, sulcated, about as long as the radius of the disk, and three times as long as broad at the base. Inner cavity of the disk simple, without centripetal rods.

Dimensions.—Diameter of the disk 0.15, of the pores 0.007; length of the polar spines 0.08, basal breadth 0.03.

Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.

Genus 178. Theodiscus,^[4] n. gen.

Definition.—Cenodiscida with three radial spines on the margin of the disk, placed in its equatorial plane.

The genus Theodiscus is the most simple form of those very numerous Discoidea in which three rays are developed on the margin of the disk; a symbol of the Christian dogma of the Trinity. Commonly the three angles between the three spines are equal, more rarely one angle is larger than the two others which are equal. The shell of some species is nearly spherical (formerly separated by me as Theosphæra), whilst in others it is a flattened biconvex lens.

Subgenus 1. Theodiscoma, Haeckel.

Definition.—Angles between the three radial spines equal (triangle equilateral).

1. Theodiscus divinus, n. sp.

Disk nearly spherical, with smooth surface. Pores regular, circular, hexagonally framed; seven to eight on the radius. Three angles between the spines equal. Spines prismatic, straight, twice as broad as one pore, eight to eleven times as long as the shell diameter.

Dimensions.—Diameter of the disk 0.1, of the pores 0.006; length of the spines 0.8 to 1.1, breadth 0.01.

Habitat.—Central Pacific, Station 265, surface.

2. Theodiscus christianus, n. sp.

Disk nearly spherical, with smooth surface. Pores regular, circular, prolonged into short cylindrical, prominent tubuli, half as high as broad; eight to nine on the radius. Three angles between the spines equal. Spines prismatic, straight, twice as broad as one pore, twelve to fifteen times as long as the shell diameter.

Dimensions.—Diameter of the disk 0.08, of the pores 0.005; length of the spines 1.1 to 1.2, breadth 0.01.

Habitat.—Central Pacific, Station 271, surface.

3. Theodiscus trinitatis, n. sp.

Disk a rather flattened, biconvex lens, about twice as broad as thick. Pores regular, circular, not prolonged into tubuli; five to six on the radius. Three angles between the spines equal. Spines pyramidal, three times as broad as one pore, about twice as long as the shell diameter.

Dimensions.—Diameter of the disk 0.06, of the pores 0.007; length of the spine 0.12, basal breadth 0.02.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

Subgenus 2. Theodiscura, Haeckel.

Definition.—Angles between the three radial spines unequal, two paired angles equal, larger or smaller than the odd angle (triangle isosceles).

4. Theodiscus vanitatis, n. sp.

Disk nearly spherical, with smooth surface. Pores irregular, roundish; eight to ten on the radius. Three angles between the spines unequal; one odd angle larger than both others. Spines pyramidal, of unequal size; one odd spine larger, both others smaller than the shell diameter.

Dimensions.—Diameter of the disk 0.12, pores 0.004 to 0.006; length of the odd spine 0.2, of the paired spines 0.1.

Habitat.—South Atlantic, Station 335, depth 1425 fathoms.

5. Theodiscus nirvana, n. sp.

Disk a flat biconvex lens, about twice as broad as thick. Pores regular, circular; ten to twelve on the radius. Three angles between the spines unequal; one odd angle smaller than both others. Spines prismatic, very long and thin, twice as broad as one pore, ten to twelve times as long as the shell diameter.

Dimensions.—Diameter of the disk 0.1, pores 0.005; length of the spines 1 to 1.2 or more, breadth 0.01.

Habitat.—Indian Ocean, Ceylon, surface, Haeckel.

Genus 179. Crucidiscus,^[5] n. gen.

Definition.—Cenodiscida with four radial spines on the margin of the disk, crossed in the equatorial plane.

The genus Crucidiscus is the most simple form of the Staurodiscida, or of the numerous Discoidea (belonging to different families) in which the margin of the disk bears four radial spines, lying in the equatorial plane, and crossed at right angles. Whilst commonly the internal shell-cavity of Crucidiscus is quite simple, in one case it bears four centripetal axial rods, as inner prolongations of the outer radial cross-spines, perhaps indications of a lost medullary shell (comp. p. 410).

Subgenus 1. Staurentodiscus, Haeckel.

Definition.—Internal cavity of the shell with centripetal axial rods.

1. Crucidiscus endostaurus, n. sp. (Pl. 48, fig. 2).

Disk with smooth surface and smooth simple margin. Pores regular, circular; thirteen to fourteen on the radius of the disk. Four crossed spines conical, strong, longer than the radius of the disk, on the inside prolonged into four thinner centripetal axial rods, which do not reach the centre. In the middle part of the disk also some other short axial rods arise from the inside, not reaching the centre (as in Stylodiscus endostylus, Pl. 31, fig. 11).

Dimensions.—Diameter of the disk 0.16, of the pores 0.004; length of the spines 0.2, breadth 0.014.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

Subgenus 2. Staurexodiscus, Haeckel.

Definition.—Internal cavity of the shell without centripetal axial rods.

2. Crucidiscus cuspidatus, n. sp.

Disk with smooth surface and simple smooth margin. Pores regular, circular; seven to eight on the radius of the disk. Four crossed spines pyramidal, with prominent edges, somewhat shorter than the radius of the disk, twice as broad at their thick base as one pore. No internal axial rods in the shell cavity.

Dimensions.—Diameter of the disk 0.12, of the pores 0.005; length of the spines 0.05, basal breadth 0.025.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

3. Crucidiscus echinatus, n. sp.

Disk with thorny surface and thorny margin. Pores regular, circular, six to seven on the radius. Four crossed spines pyramidal (four sided?), about as long as the radius of the disk, as broad at their base as one pore. No internal axial rods. Spines of the surface short, conical.

Dimensions.—Diameter of the disk 0.14, of the pores 0.008; length of the spines 0.08, basal breadth 0.02.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

4. Crucidiscus cruciatus, n. sp.

Disk with smooth surface and broad dentated margin. Pores regular, circular; eleven to twelve on the radius. Four crossed spines pyramidal, sulcated, about as long as the radius of the disk, as broad at their base as the radiated margin, which bears fifty to sixty triangular pointed teeth of irregular size. (Similar to Sethostaurus cruciatus, Pl. 31, fig. 5, but without internal axial rods and medullary shell.)

Dimensions.—Diameter of the disk 0.2, of the pores 0.007; length of the spines 0.1, basal breadth 0.02.

Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.

Genus 180. Trochodiscus,^[6] n. gen.

Definition.—Cenodiscida with numerous (ten to twenty or more) radial spines on the margin of the disk, situated in its equatorial plane.

The genus Trochodiscus bears on the thin margin of the latticed disk a variable number of radial spines (commonly ten to twenty, sometimes fifty to eighty or more). Their size and disposition are commonly more or less irregular. For the most part all the marginal spines lie in the equatorial plane; but sometimes part of them are crowded into two or four parallel girdles. Several species of this genus are very similar to some species of Heliodiscus, and only differ in the absence of the medullary shell, perhaps in consequence of the phylogenetic loss of it; if this be the case, the former are to be derived from the latter (compare p. 410).

Subgenus 1. Trochodisculus, Haeckel.

Definition.—Bases of the marginal spines free, not connected by a solid equatorial girdle.

1. Trochodiscus cenophacus, n. sp.

Disk with smooth surface. Pores regular, circular; eleven to twelve on the radius. Marginal spines sixteen to twenty, conical, of irregular size and disposition, about three times as long as broad, and as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.15, of the pores 0.006; length of the spines 0.06 to 0.09, basal breadth 0.02 to 0.03.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Trochodiscus medusinus, n. sp.

Disk with smooth surface. Pores regular, circular; nine to ten on the radius. Marginal spines ten to twelve, equilateral triangular, deeply sulcated, about half as long and broad as the radius of the disk. (Very similar to Heliosestrum medusinum, Pl. 34, fig. 6, but without enclosed medullary shell. Compare p. 410.)

Dimensions.—Diameter of the disk 0.2, of the pores 0.01; length of the spines 0.05, basal breadth 0.05.

Habitat.—North Pacific, Station 241, depth 2300 fathoms.

3. Trochodiscus odontotrochus, n. sp.

Disk with smooth surface, in the distal part radially sulcated. Pores irregular, roundish; twelve to fourteen on the radius. Marginal spines very short and numerous (thirty to forty), conical, scarcely one-fourth as long as the radius of the disk, which resembles a wheel with marginal teeth.

Dimensions.—Diameter of the disk 0.18, of the pores 0.004; length of the spines 0.02, basal breadth 0.01.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

4. Trochodiscus solaris, n. sp.

Disk with smooth surface. Pores subregular, circular; eight to nine on the radius. Marginal spines very numerous (sixty to eighty), in two to four girdles densely crowded together, the largest as long as the diameter of the disk, bent and conical. (Similar to Heliodiscus solaster, Pl. 34, fig. 4, but without medullary shell.)

Dimensions.—Diameter of the disk 0.15, of the pores 0.008; length of the spines 0.05 to 0.15, basal breadth 0.01.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

5. Trochodiscus echiniscus, n. sp.

Disk with spiny surface. Pores irregular, roundish; ten to eleven on the radius. Marginal spines conical, very numerous (forty to fifty), irregular in size and disposition, the largest half as long as the radius of the disk. (Similar to Heliodiscus echiniscus, Pl. 34, fig. 5, but without medullary shell.)

Dimensions.—Diameter of the disk 0.18, of the pores 0.005 to 0.015; length of the spines 0.02 to 0.04, basal breadth 0.01.

Habitat.—North Atlantic, Færöe Channel, John Murray.

Subgenus 2. Pristodiscus, Haeckel.

Definition.—Bases of the marginal spines connected by a solid siliceous equatorial girdle.

6. Trochodiscus stellaris, n. sp. (Pl. 48, fig. 3).

Disk with smooth surface. Pores subregular, circular; seven to eight on the radius. Marginal spines twelve to sixteen, triangular, of subregular size and disposition, about half as long as the radius of the disk, connected at their broad base by a solid equatorial girdle of half the breadth; girdle and spines radially striped.

Dimensions.—Diameter of the disk 0.25, of the pores 0.015; length of the spines 0.04 to 0.06, basal breadth 0.02 to 0.04.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

7. Trochodiscus cingillum, n. sp.

Disk with smooth surface, in the distal part radially sulcated. Pores regular, circular; twelve to thirteen on the radius. Marginal spines twenty to twenty-four, triangular, of equal size and at regular distances, only one-fourth as long as the radius of the disk, connected at their broad base by a solid equatorial girdle of the double breadth. (Similar to Heliodiscus cingillum, Pl. 33, fig. 7, but without medullary shell.)

Dimensions.—Diameter of the disk 0.22, of the pores 0.004; length of the spines 0.02, basal breadth 0.02

Habitat.—South Pacific, Station 285, depth 2375 fathoms.

Family XIX. Phacodiscida, Haeckel (Pls. 31-35).

Phacodiscida, Haeckel, 1881, Prodromus, p. 456.

Definition.—Discoidea with simple extracapsular phacoid shell (or lenticular latticed cortical shell), connected by radial beams with an intracapsular, simple or double, concentric medullary shell, without chambered equatorial girdles.

The family Phacodiscida comprises a large number of splendid forms (about a hundred species), which agree with the preceding Cenodiscida in the possession of the characteristic extracapsular "phacoid shell," but differ from them in having one or two intracapsular "medullary shells"; these concentric spherical medullary shells are connected with the lenticular cortical shell or phacoid shell by means of radial beams perforating the central capsule. The Phacodiscida bear therefore the same relation to the Cenodiscida that the Disphærida and Trisphærida do to the Monosphærida.

Formerly several species belonging to the family were described by Ehrenberg and Johannes Müller, but not distinguished from the Sphæroidea, genus Haliomma (e.g., Haliomma sol et Haliomma humboldtii of the former, Haliomma amphidiscus of the latter). For these oldest known species I constituted in 1862 my genus Heliodiscus (Monogr. d. Radiol., p. 436). Some other genera were afterwards (1875) figured by Ehrenberg as Periphæna and Chilomma. The rich material of the Challenger revealed this family as very polymorphic and widely distributed, so that in my Prodromus (1881, p. 457) I could enumerate eighteen different genera of Phacodiscida. This number is here reduced to fifteen, uniting several of them into one genus as "subgenera."

The Medullary Shell of the Phacodiscida, or the intracapsular latticed shell, is either simple and spherical, or double, composed of two concentric spheres, which are united by a variable number of radial beams. We could distinguish therefore as two subfamilies the Carpodiscida (with simple medullary shell) and the Thecodiscida (with double concentric medullary shell); the former corresponding to the Carposphærida (or Dyosphæria), the latter to the Thecosphærida (or Triosphæria). But as this difference seems not to be so important as the different shape of the disk margin, we prefer this latter as a character for the separation of subfamilies. The form of the medullary shells is commonly quite spherical (as also in the above mentioned Sphæroidea); sometimes it is a little compressed in the same direction as the enclosing lenticular phacoid shell. The diameter of the latter is commonly three to four times as large as the diameter of the medullary shell; if this be double (in the Thecodiscida) then the diameter of the outer medullary shell is commonly three to four times as large as that of the inner. The radial beams connecting the two seem to be very variable in number and disposition (compare Pl. 31, fig. 8; Pl. 32, figs. 3, 4a, 7, 8a; Pl. 33, figs. 2, 3; Pl. 35, figs. 4, 8, 9, &c.).

The Radial Beams, which connect the medullary shell with the cortical or "phacoid shell," and which pierce the membrane of the lenticular central capsule, are commonly aggregated into two polar bunches around the shortened axis of the disk (compare Pl. 31, fig. 8; Pl. 32, figs. 3, 8; Pl. 33, figs. 2, 3, &c.). Their number seems to be usually between ten and thirty. More rarely piercing radial beams lie also in the equatorial plane, and then commonly as inner prolongations of the outer marginal spines; so we find two opposite in one axis, in Heliostylus (Pl. 34, figs. 1, 2), or four opposite in pairs in two crossed axes, in Phacostaurus (Pl. 31, figs. 1, 2, 7). Often the thickness of the beams increases from the centre towards the periphery.

The Phacoid Shell, or the lenticular extracapsular cortical shell, exhibits in the Phacodiscida quite the same general character as in the Cenodiscida, above described (p. 410). Commonly the equatorial diameter of the lens is twice to three times as large as the vertical diameter or the shortened "main axis." The convexity of both opposite faces is either quite even to the sharp margin (Pl. 31, fig. 2; Pl. 33, figs. 2, 5), or the central part of the lens is more strongly vaulted, and often the margin is thickened or truncated (Pl. 31, fig. 10; Pl. 35, fig. 7). The surface of the lens is commonly smooth, but sometimes also covered with bristle-shaped radial spines (Pl. 34, figs. 3, 5; Pl. 32, figs. 2, 3); rarely these spines are prolonged and branched (Pl. 35, figs. 3, 5). The pores of the phacoid shell are usually quite regular, circular, and regularly arranged, either in more concentric or in more radial rows; the latter are sometimes separated by radial crests arising towards the margin (Pl. 35, fig. 6). If the wall of the phacoid shell be much thickened, the pores in its central part are shorter and cylindrical, in its marginal part longer and conical (Pl. 31, fig. 7; Pl. 32, fig. 1).

The Margin of the Lens of the Phacodiscida is very polymorphic, and serves mainly for the separation of genera. In the first subfamily, Sethodiscida, it is either quite simple (Pl. 35, figs. 6-8) or surrounded by a thin solid equatorial girdle, the basal part of which is often radially striped (Pl. 32, figs. 7, 8). In the second subfamily, Heliosestrida, we find on the margin a small number of radial spines in the equatorial plane regularly disposed, either two opposite in one axis (Pl. 31, figs. 9-12) or four opposite in pairs in two crossed axes (Pl. 31, figs. 1-8), or eight opposite in pairs in four axes, crossed at angles of 45° (Pl. 34, figs. 3, 6); in the latter case we can sometimes distinguish (as in many Medusæ) four larger perradial spines alternating with four smaller interradial spines. Often in one and the same species occur abnormalities in number and disposition of the radial spines, three or five spines instead of four, or also seven or nine spines instead of eight; often both halves of the disk become asymmetrical. If the number of the marginal spines exceed eight to ten, they commonly become very variable in size and irregular in disposition; these variations characterise the third subfamily, Heliodiscida. Commonly also here all spines lie in the equatorial plane; but sometimes they become crowded in several parallel circles on both sides of the margin (Pl. 32, fig. 1). The form of the marginal spines is commonly conical or flattened triangular, often also pyramidal or deeply furrowed (Pl. 31, figs. 6-9). Very rarely the spines are fenestrated (Pl. 35, fig. 1); only in one genus (Heliodrymus) they are all or partly branched (Pl. 33, fig. 9; Pl. 35, figs. 3, 5).

The peculiar development of the phacoid shell has been already described by J. Müller (compare my Monograph, 1862, pp. 156, 438).

The Central Capsule of the Phacodiscida is everywhere circular, lenticular, envelops the medullary shell, and is enclosed by the phacoid shell, perforated by the radial beams, which connect the latter to the former.

Synopsis of the Genera of the Phacodiscida.

III. Subfamily Sethodiscida. Margin of the disk without radial spines.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Margin simple, without equatorial girdle.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Medullary shell simple,	181. Sethodiscus.
				Medullary shell double,	182. Phacodiscus.
		Margin surrounded by a hyaline equatorial girdle.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Medullary shell simple,	183. Periphæna.
				Medullary shell double,	184. Perizona.
III. Subfamily Heliosestrida. Margin of the disk with two to eight solid radial spines, usually quite regularly disposed. (Number usually constant.)	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Two radial spines (opposite in one axis).	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Medullary shell simple,	185. Sethostylus.
				Medullary shell double,	186. Phacostylus.
		Three radial spines.		Medullary shell simple,	187. Triactiscus.
		Four radial spines (in cross form).	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Medullary shell simple,	188. Sethostaurus.
				Medullary shell double,	189. Phacostaurus.
		Six radial spines.		Medullary shell simple,	190. Distriactis.
		Eight radial spines.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Medullary shell simple,	191. Heliosestrum.
				Medullary shell double,	192. Astrosestrum.
III. Subfamily Heliodiscida. Margin of the disk with numerous (ten to twenty or more) radial spines, usually irregularly disposed. (Number variable.)	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Radial spines all simple, not branched.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Medullary shell simple,	193. Heliodiscus.
				Medullary shell double,	194. Astrophacus.
		Radial spines all or partly		Medullary shell simple,	195. Heliodrymus.

Subfamily 1. Sethodiscida, Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida without radial spines on the margin of the disk.

Genus 181. Sethodiscus,^[7] Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with simple medullary shell and simple margin of the circular disk, without surrounding equatorial girdle and without radial spines.

The genus Sethodiscus is the most simple and primitive form of all Phacodiscida, and may be regarded as the common ancestral form of this family. The simple spherical medullary shell is connected by a variable number of radial beams with the lenticular or discoidal cortical shell (or "phacoid shell"). The margin of this latter is quite simple, circular, without solid equatorial girdle or radial spines. From the nearly allied genus Carposphæra of the Sphæroidea, its probable ancestral form, Sethodiscus can be derived simply by lenticular compression of the spheroidal cortical shell.

Subgenus 1. Sethodiscinus, Haeckel.

Definition.—Surface of the disk smooth, without radial ribs or spines.

1. Sethodiscus phacoides, n. sp.

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; fourteen to fifteen on the radius of the disk. (Very similar to Periphæna cincta, Pl. 33, fig. 4, but without the girdle of the margin.)

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.07, of the pores 0.005.

Habitat.—Pacific, central area, Stations 270 to 274, in various depths.

2. Sethodiscus macroporus, n. sp.

Disk with smooth surface, twice as broad as the medullary shell. Pores regular, circular, very large; five to six on the radius of the disk. (Remarkable for the extraordinary size of the pores, which reaches half the radius of the medullary shell.)

Dimensions.—Diameter of the disk 0.1, of the medullary shell 0.05, of the pores 0.012.

Habitat.—North Atlantic, Gulf Stream, Færöe Channel, John Murray.

3. Sethodiscus microporus, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular, very small; twenty-two to twenty-four on the radius of the disk. (The small pores are scarcely half as broad as the thick bars between them.)

Dimensions.—Diameter of the disk 0.25, of the medullary shell 0.06, of the pores 0.002.

Habitat.—South Pacific, Station 288, surface.

4. Sethodiscus lenticula, n. sp. (Pl. 33, figs. 1, 2).

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, polygonal; eight to nine on the radius of the disk. (The pores of the medullary shell, fig. 2, are also irregular, polygonal, or roundish.)

Dimensions.—Diameter of the disk 0.17, of the medullary shell 0.04, of the pores 0.01.

Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.

5. Sethodiscus macrococcus, n. sp. (Pl. 33, fig. 3).

Disk with smooth surface, two and a half times as broad as the medullary shell. Pores irregular, polygonal; eleven to twelve on the radius of the disk. (The pores of the medullary shell, fig. 3, are regular, circular, with elevated hexagonal frames between them. The figured specimen is a young one, both halves of the biconvex disk being not yet united in the equatorial plane.)

Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.065, of the pores 0.01.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

6. Sethodiscus micrococcus, n. sp.

Disk with smooth surface, five times as broad as the medullary shell. Pores irregular, roundish, very small; twenty-six to twenty-eight on the radius of the disk. (The pores of the small medullary shell are regularly circular, of the same size as those of the disk.)

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.04, of the pores 0.002.

Habitat.—South Atlantic, Station 335, depth 1425 fathoms.

Subgenus 2. Sethodisculus, Haeckel.

Definition.—Surface of the disk with elevated radial ribs or spines.

7. Sethodiscus radiatus, Haeckel.

Haliomma radians, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 50. Haliomma radiatum, Ehrenberg, 1854, Mikrogeol., Taf. xxi. fig. 54.

Disk with radiated surface, four times as broad as the medullary shell. Pores regularly circular; nine to ten on the radius of the disk, arranged in radial series (about forty), which are separated by smooth crests, not prominent on the smooth margin.

Dimensions.—Diameter of the disk 0.12, of the medullary shell 0.03, of the pores 0.003.

Habitat.—Fossil in Tertiary deposits of the Mediterranean, Greece, Sicily, Oran, &c.

8. Sethodiscus echinatus, Haeckel.

Haliomma echinatum, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. fig. 2.

Disk with radiated thorny surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius of the disk, arranged in radial series (about sixty), which are separated by thorny crests, prominent a little on the dentated margin.

Dimensions.—Diameter of the disk 0.18, of the medullary shell 0.06, of the pores 0.01.

Habitat.—Fossil in the rocks of Barbados.

9. Sethodiscus cristatus, n. sp.

Disk with radiated surface, four times as broad as the medullary shell. Pores regularly circular; sixteen to seventeen on the radius of the disk, arranged in radial series (about eighty), which are separated in the distal half by smooth elevated crests, strongly prominent on the dentated margin. (Very similar to Phacodiscus cristatus, Pl. 35, fig. 6, but with simple medullary shell.)

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05, of the pores 0.005.

Habitat.—South Pacific, Station 285, depth 2375 fathoms.

Genus 182. Phacodiscus,^[8] Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with double medullary shell and simple margin of the circular disk, without surrounding equatorial girdle and without radial spines.

The genus Phacodiscus differs from the ancestral genus Sethodiscus only in the duplication of the medullary shell, and has therefore the same relation to it that Thecosphæra in the Sphæroidea exhibits to Carposphæra. Both former discoidal genera differ from the two latter spheroidal by the lenticular flattening of the cortical shell.

Subgenus 1. Phacodiscinus, Haeckel.

Definition.—Surface of the disk smooth, without radial ribs or spines.

1. Phacodiscus rotula, n. sp. (Pl. 35, fig. 7).

Disk with smooth surface, four and a half times as broad as the outer and fourteen times as broad as the inner medullary shell. Pores regularly circular; sixteen to eighteen on the radius of the disk. Margin of the lens very thick, truncated, nearly as broad as the outer medullary shell.

Dimensions.—Diameter of the disk 0.21, of the outer medullary shell 0.045, of the inner 0.015; pores 0.008.

Habitat.—North Pacific, Station 224, depth 1850 fathoms.

2. Phacodiscus lentiformis, n. sp. (Pl. 35, fig. 8).

Disk with smooth surface, three and a half times as broad as the outer, and ten times as broad as the inner medullary shell. Pores regularly circular; twelve to thirteen on the radius of the disk. Margin of the disk sharp, as in a biconvex lens.

Dimensions.—Diameter of the disk 0.25, of the outer medullary shell 0.07, of the inner 0.025; pores 0.01.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms; fossil in Barbados.

3. Phacodiscus grandis, n. sp.

Disk with thorny surface, five times as broad as the outer, and fifteen times as broad as the inner medullary shell. Pores regularly circular; twenty-two to twenty-four on the radius of the disk. Margin of the disk thick, rounded.

Dimensions.—Diameter of the disk 0.45, of the outer medullary shell 0.09, of the inner 0.03; pores 0.01.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

Subgenus 2. Phacodisculus, Haeckel.

Definition.—Surface of the disk with elevated radial ribs or spines.

4. Phacodiscus echiniscus, n. sp.

Disk with spiny surface, four times as broad as the outer, and ten times as broad as the inner medullary shell. Pores irregularly roundish; fourteen to fifteen on the radius of the disk. Margin of the disk sharp, as in a biconvex lens.

Dimensions.—Diameter of the disk 0.3, of the outer medullary shell 0.75, of the inner 0.03; pores 0.007.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

5. Phacodiscus clypeus, n. sp. (Pl. 35, figs. 6, 9).

Disk with radiated surface, four times as broad as the outer, and twelve times as broad as the inner medullary shell. Pores regularly circular; sixteen to eighteen on the radius of the disk; in the distal half disposed in sixty to seventy radial series, which are separated by prominent crests; the sharp margin therefore a little jagged.

Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.05, of the inner 0.017; pores 0.006.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

Genus 183. Periphæna,^[9] Ehrenberg, 1873 Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 246.

Definition.—Phacodiscida with simple medullary shell, without radial spines, but with a solid equatorial girdle around the margin of the lenticular disk.

The genus Periphæna, founded by Ehrenberg in 1873 for the fossil Periphæna decora of Barbados, differs from its ancestral form Sethodiscus in the development of a very thin siliceous solid girdle around the margin of the lenticular disk; this girdle lies in the equatorial plane of the shell, and reappears in similar form in Perichlamydium among the Porodiscida, in Spongophacus among the Spongodiscida, and in Zonodiscus among the Cenodiscida.

1. Periphæna cincta, n. sp. (Pl. 33, fig. 4).

Disk with smooth surface, four times as broad as the medullary shell. Pores regularly circular; fourteen to sixteen on the radius of the disk. Girdle of the margin about half as broad as the radius of the medullary shell, in the distal half structureless, in the proximal half with seventy to eighty short radial ribs.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05, of the pores 0.005.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

2. Periphæna decora, Ehrenberg.

Periphæna decora, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 80, Taf. xxviii. fig. 6.

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; twenty to twenty-two on the radius of the disk, disposed in radial series. Girdle of the margin nearly as broad as the radius of the medullary shell, in the distal half structureless, in the proximal half with eighty to ninety short radial ribs.

Dimensions.—Diameter of the disk 0.25, of the medullary shell 0.08, of the pores 0.06.

Habitat.—Fossil in Barbados.

3. Periphæna statoblastus, n. sp.

Disk with smooth surface, five times as broad as the medullary shell. Pores regularly circular; twenty-four to twenty-six on the radius of the disk, disposed in radial series, those in the distal half of the disk being separated by piercing radial beams. Girdle of the margin twice as broad as the radius of the medullary shell, in the whole breadth with one hundred and twenty to one hundred and thirty piercing radial ribs, the prolongations of the beams.

Dimensions.—Diameter of the disk 0.3, of the medullary shell 0.06, of the pores 0.04.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

Genus 184. Perizona,^[10] Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with double medullary shell, without radial spines, but with a solid equatorial girdle around the margin of the lenticular disk.

The genus Perizona differs from its ancestral form Phacodiscus in the development of a thin solid siliceous girdle, lying in the equatorial plane around the margin of the disk. The two genera bear the same relation to each other that Periphæna bears to Sethodiscus. But in the two latter genera the spherical medullary shell is simple, in the two former double.

1. Perizona scutella, n. sp. (Pl. 32, fig. 7).

Disk with smooth surface, in the distal third radiated, four times as broad as the outer, and ten times is broad as the inner medullary shell. Pores subregular, circular; thirteen to fourteen on the radius of the disk, in the marginal part separated by eighty to ninety prominent radial crests, which are prolonged into the proximal half of the solid girdle. Breadth of the girdle equal to that of the inner medullary shell.

Dimensions.—Diameter of the disk 0.25, of the outer medullary shell 0.06, of the inner 0.025; pores 0.007.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

2. Perizona pterygota, n. sp. (Pl. 32, figs. 8, 8a).

Disk with smooth surface, six times as broad as the outer, and fifteen times as broad as the inner medullary shell. Pores regularly circular; eighteen to twenty on the radius of the disk. Margin much thickened and truncated, abruptly separated in the equatorial circumference from the peripheral sharp margin of the solid girdle; breadth of the girdle equal to that of the outer medullary shell.

Dimensions.—Diameter of the disk 0.25, of the outer medullary shell 0.04, of the inner 0.015; pores 0.006.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

Subfamily 2. Heliosestrida, Haeckel.

Definition.—Phacodiscida with a constant number of radial spines on the margin of the disk (two, three, four, six, or eight), which are commonly regularly disposed (sometimes more or less irregularly).

Genus 185. Sethostylus,^[11] Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with simple medullary shell and with two radial spines on the margin of the disk, opposite in the equatorial axis.

The genus Sethostylus opens the series of the Heliosestrida or of those Phacodiscida in which a constant number of radial spines (two to eight) is more or less regularly disposed on the margin of the disk. All these marginal spines lie in the equatorial plane of the lens, and have in the same species a rather constant number and similar size, a certain form and disposition. Sometimes they incline more or less to irregular variations. In Sethostylus there are only two spines, opposite in the equatorial diameter of the lens; it corresponds to Stylocyclia among the Coccodiscida, and to Xiphodictya among the Porodiscida.

Subgenus 1. Sethostylium, Haeckel.

Definition.—Margin of the disk simple, smooth, without equatorial girdle and without a corona of marginal spines.

1. Sethostylus distyliscus, n. sp. (Pl. 31, fig. 9).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; nine to ten on the radius of the disk, in the outer rows cylindrical. Margin of the disk simple, smooth, thin, without peculiar equatorial girdle, radially striped by the prominent beams of the peripheral series of pores. Both marginal spines of equal size, pyramidal, sulcated, about as long as the radius of the disk and as broad at the base as the medullary shell.

Dimensions.—Diameter of the disk 0.13 to 0.16, of the medullary shell 0.04 to 0.05; length of both opposite spines 0.06 to 0.08, basal breadth 0.03 to 0.04.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

2. Sethostylus dicylindrus, n. sp. (Pl. 31, fig. 10).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; sixteen to eighteen on the radius of the disk. Margin of the disk simple, smooth, thick, without peculiar equatorial girdle. Both marginal spines cylindrical, about as long as the diameter of the disk, about twice as broad as a single pore. (Walls of the disk in the central part twice to three times as thick as in the peripheral part.)

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of both spines 0.2 to 0.3, breadth 0.008.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

Subgenus 2. Heliostylus, Haeckel, 1881, Prodromus, p. 457.

Definition.—Margin of the disk with a solid equatorial girdle or a corona of radial spines.

3. Sethostylus dentatus, n. sp. (Pl. 34, fig. 1).

Heliostylus dentatus, Haeckel, 1881, Prodromus et Atlas (pl. xxxiv. fig. 1).

Disk with smooth surface, six times as broad as the medullary shell. Pores regular, circular; eighteen to twenty on the radius of the disk. Margin of the disk with a broad solid equatorial girdle, which bears fifty to sixty strong conical teeth on the periphery; teeth about as long as the diameter of the medullary shell. Both opposite marginal spines cylindro-conical, about as long as the diameter of the disk, and as broad as the girdle.

Dimensions.—Diameter of the disk 0.3, of the medullary shell 0.05; length of both main spines 0.2 to 0.3, breadth 0.02.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

4. Sethostylus serratus, n. sp. (Pl. 34, fig. 2).

Heliostylus serratus, Haeckel, 1881, Prodromus et Atlas (pl. xxxiv. fig. 2).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; fourteen to sixteen on the radius of the disk. Margin with a broad solid equatorial girdle, which bears forty to fifty strong conical teeth on the periphery; teeth about as long as the radius of the medullary shell. Both opposite marginal spines spindle-shaped, about as long as the diameter of the disk, and as broad as the girdle.

Dimensions.—Diameter of the disk 0.3, of the medullary shell 0.075; length of both main spines 0.2 to 0.3, breadth 0.03.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

5. Sethostylus hastatus, n. sp.

Disk with smooth surface, two and a half times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius of the disk. Margin with a broad solid equatorial girdle, which bears on the periphery six conical teeth, three on each half between the two main spines, which are cylindrical, longer than the diameter of the disk, and half as broad as the girdle. (This species can be derived from Heliosestrum, two opposite spines of the eight marginal spines being much stronger developed than the other six.)

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.06; length of both main spines 0.2, breadth 0.01.

Habitat.—North Atlantic, Station 354, surface.

6. Sethostylus spicatus, n. sp.

Disk with spiny surface, four times as broad as the medullary shell. Pores irregular roundish, with many unequal conical spines between them. Margin with an equatorial girdle, composed of three to four concentric series of conical radial spines, about as long as the radius of the medullary shell. Both main spines very large, cylindrical, longer than the diameter of the disk, and as broad as the radius of the medullary shell.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the main spines 0.3 or more, breadth 0.025.

Habitat.—Fossil in the rocks of Barbados, Haeckel; living in the depths of the Equatorial Atlantic, Station 348, depth (2450) fathoms.

Genus 186. Phacostylus,^[12] Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with double medullary shell and with two radial spines on the margin of the disk, opposite in the equatorial axis.

The genus Phacostylus differs from the foregoing Sethostylus by the duplication of the medullary shell, and bears the same relation to it as Phacodiscus does to Sethodiscus, or as Amphicyclia in the Coccodiscida does to Stylocyclia.

Subgenus 1. Phacostylium, Haeckel.

Definition.—Margin of the disk simple, smooth, without equatorial girdle, and without a corona of marginal spines.

1. Phacostylus amphistylus, n. sp. (Pl. 31, fig. 12).

Disk with smooth surface, four times as broad as the outer, and twelve times as broad as the inner medullary shell. Pores regular, circular; twelve to fourteen on the radius of the disk. Margin of the disk simple, smooth, without spines and equatorial girdle. Both polar spines conical, longer than the diameter of the disk, furrowed at the base, and twice as broad as the inner medullary shell.

Dimensions.—Diameter of the disk 0.16 to 0.18, of the outer medullary shell 0.045, of the inner 0.015; length of the polar spines 0.2, basal breadth 0.03.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

2. Phacostylus amphixiphus, n. sp.

Disk with smooth surface, three times as broad as the outer, and eight times as broad as the inner medullary shell. Pores irregular, roundish; ten to eleven on the radius. Margin of the disk simple, smooth, without spines and equatorial girdle. Both polar spines sword-shaped triangular, two-edged, about as long as the radius of the disk, and as broad at the base as the inner medullary shell.

Dimensions.—Diameter of the disk 0.15, of the outer medullary shell 0.05, of the inner 0.02; length of the polar spines 0.08, basal breadth 0.02.

Habitat.—Indian Ocean, Madagascar, Rabbe, surface.

Subgenus 2. Astrostylus, Haeckel.

Definition.—Margin of the disk with a solid equatorial girdle or a corona of radial spines.

3. Phacostylus amphipyramis, n. sp.

Disk with spiny surface, four and a half times as broad as the outer, and fourteen times as broad as the inner medullary shell. Pores irregular, roundish; eight to ten on the radius. Margin of the disk with a corona of irregular, radial spines. Both opposite polar spines pyramidal, twice as long as broad, and nearly as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.22, of the outer medullary shell 0.05, of the inner 0.016; length of the polar spines 0.1, basal breadth 0.05.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

4. Phacostylus caudatus, n. sp. (Pl. 32, fig. 6).

Astrosestrum caudatum, Haeckel, 1881, Prodromus et Atlas (pl. xxxii. fig. 6).

Disk with smooth surface, two and a half times as broad as the outer, and six times as broad as the inner medullary shell. Pores regular, circular; six to seven on the radius of the disk. Margin with a solid equatorial girdle, and irregularly bordered with eight to ten conical spines; two opposite of these are much longer than the others. (This species can be derived from Astrosestrum, two opposite marginal spines being much more strongly developed than the six to eight others.)

Dimensions.—Diameter of disk 0.12, of the outer medullary shell 0.05, of the inner 0.02; length of the polar spines 0.1 to 0.25, basal breadth 0.025.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

5. Phacostylus maximus, n. sp.

Disk with smooth surface, five times as broad as the outer, and ten times as broad as the inner medullary shell. Pores regular, circular; twenty to twenty-two on the radius. Margin with a solid equatorial girdle, bearing on the periphery one hundred to one hundred and twenty plain teeth, and two very large polar spines, which are cylindrical, longer than the diameter of the disk, and as broad at the furrowed base as the radius of the outer medullary shell. (Similar to Sethostylus dentatus, Pl. 34, fig. 1, but much larger, and with a double medullary shell.)

Dimensions.—Diameter of the disk 0.4, of the outer medullary shell 0.08, of the inner 0.04; length of the polar spines 0.5, basal breadth 0.04.

Habitat.—Fossil in the rocks of Barbados.

Genus 187. Triactiscus,^[13] Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with simple medullary shell, and with three radial spines on the margin of the disk, placed in the equatorial plane.

The genus Triactiscus exhibits on the margin of the lenticular phacoid shell three radial solid spines, the distance between which is sometimes equal, at other times unequal. Either all the three spines are of equal size and similar form, or one odd arm is smaller than the two paired arms. The triradial form of this genus is repeated in Tripodocyclia among the Coccodiscida, and in Tripodictya among the Porodiscida. The medullary shell of Triactiscus is simple.

1. Triactiscus tripyramis, n. sp. (Pl. 33, fig. 6).

Disk with smooth surface and smooth margin, three times as broad as the medullary shell. Pores regular, circular; twelve to thirteen on the radius of the disk. Three radial spines of nearly equal size and equidistant, or one odd spine a little smaller, and the opposite angle (between the paired spines) also smaller. Spines pyramidal, with broad prominent edges, one to one and a half times as long as the radius of the disk, as broad at the base as the radius of the medullary shell.

Dimensions.—Diameter of the disk 0.15; of the medullary shell 0.05, pores 0.006.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

2. Triactiscus tricuspis, n. sp. (Pl. 33, fig. 5).

Disk with smooth surface and smooth margin, five times as broad as the medullary shell. Pores irregular, roundish; ten to eleven on the radius of the disk. Three radial spines of unequal size and at unequal distances, very short, conical, not longer than the radius of the medullary shell.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.03; pores 0.004 to 0.008.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

3. Triactiscus tripodiscus, Haeckel.

Haliomma triactis, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 236, Taf. xxviii. fig, 4.

Disk with thorny surface and spiny margin, three times as broad as the medullary shell. Pores regular, circular; eight to nine on the radius of the disk. Three radial spines of different size and at unequal distances, one odd spine as long as the radius, both paired spines as long as the diameter of the disk; the odd angle between the latter is smaller. Spines pyramidal, with broad edges.

Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.05, pores 0.008.

Habitat.—Fossil in the rocks of Barbados.

Genus 188. Sethostaurus,^[14] Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with simple medullary shell and with four radial spines on the margin of the disk, crossed in the equatorial plane.

The genus Sethostaurus exhibits four marginal spines, which form commonly a more or less regular cross in the equatorial plane. Sometimes the size and disposition of the four spines become more or less different, and also the angles between them vary; the regular rectangular cross passes over into a bilateral or irregular form. The medullary shell is simple. The same cross-form of the disk is seen in Staurocyclia among the Coccodiscida, and in Staurodictya among the Porodiscida.

Subgenus 1. Sethostaurium, Haeckel.

Definition.—Margin of the disk without a solid equatorial girdle or a corona of spines.

1. Sethostaurus orthostaurus, n. sp. (Pl. 31, figs. 1, 2).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; thirteen to fourteen on the radius of the disk. Margin simple, smooth, without girdle. Four crossed spines equal, pommel-shaped, angular, contracted at the base, scarcely as long as the diameter of the medullary shell.

Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.05; length of the crossed spines 0.04, breadth 0.02.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

2. Sethostaurus conostaurus, n. sp. (Pl. 34, figs. 7, 8).

Disk with spiny surface, three times as broad as the medullary shell. Pores irregular, roundish; seven to eight on the radius. Margin simple, smooth, without girdle. Four crossed spines subregular, equal, conical, about as long as the diameter and as broad at the base as the radius of the medullary shell. (Fig. 7 exhibits the normal form, fig. 8 an abnormality with five spines.)

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.06; length of the crossed spines 0.05, basal breadth 0.03.

Habitat.—South Atlantic, Station 333, surface.

3. Sethostaurus rhombostaurus, n. sp. (Pl. 31, fig. 4).

Disk with smooth surface, two and a half times as broad as the medullary shell. Pores regular, circular; ten to eleven on the radius. Margin simple, smooth, without girdle. Two opposite spines longer than the diameter of the disk, four times as long as the two others, which only equal its radius. Spines sword-shaped, angular.

Dimensions.—Diameter of the disk 0.14, of the medullary shell 0.06; length of the major spines 0.2, of the minor 0.05, breadth 0.025.

Habitat.—North Atlantic, Station 353, depth 2965 fathoms.

4. Sethostaurus recurvatus, n. sp. (Pl. 31, fig. 3).

Disk with smooth surface, three times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Margin simple, smooth, without girdle. Four spines cylindrical, irregularly curved, of different sizes; one single very large, much longer than the three others; two opposite lateral spines recurved, hook-shaped.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the major spine 0.32, of the opposite spine 0.16, of both lateral spines 0.08.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

Subgenus 2. Heliostaurus, Haeckel 1881, Prodromus, p. 457.

Definition.—Margin of the disk with a solid equatorial girdle or a corona of spines.

5. Sethostaurus cruciatus, n. sp. (Pl. 31, fig. 5).

Heliostaurus cruciatus, Haeckel, 1881, Prodromus et Atlas (pl. xxxi. fig. 5).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius. Margin with a solid, radially striped girdle, which bears on the periphery forty to fifty triangular pointed teeth of unequal length. Four crossed spines of equal size and similar form, pyramidal, sulcated, about as long as the radius of the disk, as broad at the base as the girdle.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.06; length of the crossed spines 0.1, basal breadth 0.02.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

6. Sethostaurus coronatus, n. sp.

Disk with spiny surface, twice as broad as the medullary shell. Pores irregular, roundish; nine to ten on the radius. Margin of the disk with a solid broad girdle, bearing on the periphery a corona of thirty to forty flat tongue-shaped teeth of different length. Four crossed spines prismatic with prominent edges, about as long as the diameter of the disk, and as broad as the girdle.

Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.08, length of the crossed spines 0.18, breadth 0.02.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

7. Sethostaurus gigas, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; twenty to twenty-two on the radius. Margin of the disk with a narrow solid girdle, bearing on the periphery one hundred to one hundred and twenty slender flat pointed teeth. Four crossed spines equal, conical, about as long as the radius of the disk, as broad at their furrowed base as the radius of the medullary shell.

Dimensions.—Diameter of the disk 0.4, of the medullary shell 0.1; length of the crossed spines 0.5, basal breadth 0.05.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

Genus 189. Phacostaurus,^[15] Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with double medullary shell and with four radial spines on the margin of the disk, crossed in the equatorial plane.

The genus Phacostaurus differs from the foregoing Sethostaurus by the duplication of the medullary shell, and bears to it the same relation as Phacodiscus does to Sethodiscus. Also in this genus the cross of the shell is commonly regular, rectangular, sometimes more or less irregular.

Subgenus 1. Phacostaurium, Haeckel.

Definition.—Margin of the disk without a solid equatorial girdle or a corona of spines.

1. Phacostaurus oceanidum, n. sp. (Pl. 31, fig. 6).

Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; eleven to twelve on the diameter of the disk. Margin smooth. Four crossed spines pyramidal, deeply sulcate, about as long as the diameter of the outer medullary shell, and two-thirds as broad at the base.

Dimensions.—Diameter of the disk 0.15, of the outer medullary shell 0.05, of the inner 0.02; length of the spines 0.05, basal breadth 0.03.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

Subgenus 2. Astrostaurus, Haeckel, 1881, Prodromus, p. 457.

Definition.—Margin of the disk with a solid equatorial girdle, or a corona of spines.

2. Phacostaurus quadrigatus, n. sp.

Disk with smooth surface, four times as broad as the outer and ten times as broad as the inner medullary shell. Pores irregular, roundish; fifteen to sixteen on the diameter of the disk. Margin with a broad solid equatorial girdle, from which arise four crossed spines, conical, as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.05, of the inner 0.02; length of the spines 0.1, basal breadth 0.03.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

3. Phacostaurus magnificus, n. sp. (Pl. 31, figs. 7, 8).

Astrostaurus magnificus, Haeckel, 1881, Prodromus et Atlas (pl. xxxi. figs.7, 8).

Disk with smooth surface, three times as broad as the outer and nine times as broad as the inner medullary shell. Pores regular, circular; thirteen to fourteen on the diameter of the disk. Margin with a corona of fifty to sixty conical spines of unequal length. Four spines of the cross very large pyramidal, deeply sulcated, longer than the radius of the disk, and as broad at the base as the radius of the medullary shell.

Dimensions.—Diameter of the disk 0.22, of the outer medullary shell 0.07, of the inner 0.025; length of the four spines 0.16, basal breadth 0.04.

Habitat.—Indian Ocean, Madagascar, Rabbe, surface.

Genus 190. Distriactis,^[16] n. gen.

Definition.—Phacodiscida with simple medullary shell and with six radial spines on the margin of the disk placed in the equatorial plane.

The genus Distriactis exhibits on the margin of the lenticular phacoid shell six radial solid spines. Their distance is commonly equal, rarely unequal. Either all six spines are of equal size and similar form, or three larger (perradial) alternating with three smaller (interradial), so that Distriactis appears to be derived from Triactiscus by development of three secondary between three primary spines.

1. Distriactis liriantha, n. sp.

Disk smooth, four times as broad as the medullary shell, with regular, circular pores (about ten on the radius). Six marginal spines of equal size and at equal distances, triangular, sulcate, half as long as the radius. (Similar to Heliosestrum medusinum, Pl. 34, fig. 6.)

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the spines 0.05, basal breadth 0.04.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

2. Distriactis corallantha, n. sp.

Disk thorny, three times as broad as the medullary shell, with regular, circular pores, about eight on the radius. Six marginal spines of equal size and equidistant, conical, nearly as long as the diameter of the disk, half as broad at the base as the medullary shell.

Dimensions.—Diameter of the disk 0.12, of the medullary shell 0.04; length of the spines 0.1, breadth 0.02.

Habitat.—South Pacific, Station 300, surface.

3. Distriactis alterna, n. sp.

Disk smooth, five times as broad as the medullary shell, about twelve pores on the radius. Six marginal spines pyramidal, at equal distances, but unequal alternating size; three larger (perradial) spines as long as the shell radius, three smaller between them (interradial) half as long and broad.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.03; length of the three major spines 0.08, of the three minor 0.05.

Habitat.—North Atlantic, Station 353, surface.

4. Distriactis palmantha, n. sp.

Disk rough, four times as broad as the medullary shell, about ten pores on the radius. Six marginal spines conical, at equal distances, but unequal alternating size; three larger (perradial) spines as long as the shell diameter, three smaller between them (interradial) as long as the radius.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the three major spines 0.2, of the three minor 0.1,

Habitat.—South Atlantic, Station 325, surface.

5. Distriactis amphithecta, n. sp.

Disk thorny, three times as broad as the medullary shell. Six marginal spines conical, of very different size; one single (anterior) much larger than the five others, the opposite (posterior) much smaller. The other four spines are paired, the anterior pair larger than the posterior.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the longest spine 0.2, of the shortest 0.04, of the anterior pair 0.1, of the posterior 0.07.

Habitat.—Indian Ocean, Cocos Islands, surface, Rabbe.

Genus 191. Heliosestrum,^[17] Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with simple medullary shell and with eight radial spines on the margin of the disk (more or less regularly disposed, sometimes seven or nine).

The genus Heliosestrum (with simple medullary shell) and the following Astrosestrum (with double medullary shell) contain those Phacodiscida in which the margin of the lenticular disk bears eight radial spines, commonly more or less regularly disposed in the equatorial plane, so that the equal angles between them amount to 45°. There are, however, many exceptions to this regular eight-rayed form, either the angles between the eight spines becoming unequal or the number of the spines amounting to seven or nine (sometimes also six or ten) in one and the same species. But the regular form is as prevalent, and also in the abnormal forms indicated by the position of the spines, that we separate the genus Heliosestrum from Heliodiscus. Both genera are rich in common species, and in some of the former four perradial (larger) spines alternate regularly with four interradial (smaller) spines.

Subgenus 1. Heliosestantha, Haeckel.

Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines free, not connected by an equatorial girdle.

1. Heliosestrum medusinum, n. sp. (Pl. 34, fig. 6).

Heliodiscus medusinus, Haeckel, 1881, Atlas (pl. xxxiv. fig. 6).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; about ten on the radius of the disk. Eight marginal spines regularly distributed (sometimes seven or nine, more or less irregular), angular, nearly pyramidal (with equilateral triangular outline), about as long and broad as the diameter of the medullary shell, without connecting equatorial girdle. From the broad base of each spine run eight to ten deep furrows convergent to its apex.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.05, basal breadth 0.05.

Habitat.—North Pacific, Station 266, surface.

2. Heliosestrum octastrum, n. sp.

Disk with smooth surface, three times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Eight marginal spines regularly distributed (sometimes seven or nine, more or less irregular), conical, about as long as the diameter of the disk, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the radial spines 0.16, basal breadth 0.01.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

3. Heliosestrum solarium, Haeckel.

Haliomma sol (partim), Ehrenberg, 1875 (non 1844), Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxviii. fig. 1.

Surface of the disk smooth; its diameter six times as large as that of the medullary shell. Pores regular, circular; nine to ten on the radius. Eight marginal spines regularly distributed (sometimes seven or nine, more or less irregular), conical, about as long as the diameter of the medullary shell, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.18, of the medullary shell 0.03; length of the radial spines 0.03, basal breadth 0.01.

Habitat.—Fossil in the Tertiary rocks of Barbados.

4. Heliosestrum liriope, n. sp.

Surface of the disk smooth; its diameter four times as large as that of the medullary shell. Pores subregular, circular; seven to eight on the radius. Eight marginal spines regularly distributed, conical, compressed, alternating longer and shorter; the longer equal to the diameter of the disk, the shorter to the radius.

Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.4; length of the major radial spines 0.15, of the minor 0.09.

Habitat.—North Pacific, Station 236, surface.

5. Heliosestrum quadrigeminum, n. sp.

Surface of the disk smooth; its diameter four times as large as that of the medullary shell. Pores irregular, roundish; six to seven on the radius. Eight marginal spines triangular, flat, regularly disposed, alternating longer and shorter, the major as long as the radius of the shell, and half as broad at the base, with three to four deep furrows on both sides, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.04; length of the larger radial spines 0.08, of the smaller 0.04, basal breadth 0.04.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

6. Heliosestrum contiguum, Haeckel.

Haliomma contiguum, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. fig. 5.

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish, touching, with very thin bars; nine to ten on the radius. Eight marginal spines (often seven or nine) conical, half as long as the radius, twice as long as broad, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.17, of the medullary shell 0.04; length of the radial spines 0.04, basal breadth 0.02.

Habitat.—Fossil in Barbados.

7. Heliosestrum irregulare, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; nine to eleven on the radius. Eight conical radial spines of irregular size and distribution, often seven or nine, about as long as the radius of the disk (in some cases longer, in others shorter). No connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.1, basal breadth 0.02.

Habitat.—Central Pacific, Stations 270 to 272, depth 2425 to 2925 fathoms.

Subgenus 2. Heliosestilla, Haeckel.

Definition.—Surface of the disk armed with radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

8. Heliosestrum octonum, n. sp. (Pl. 34, fig. 3).

Disk with spiny surface, three times as broad as the medullary shell. Pores circular, of very different sizes; eight to ten on the radius. Eight conical marginal spines of equal size and equidistant, as long as the radius of the disk, and one-third as broad at the base as the medullary shell. Numerous spines on the surface bristle-shaped, on the margin half as long as the eight main spines, in the central part shorter.

Dimensions.—Diameter of the disk 0.18, of the medullary shell 0.06; length of the marginal spines 0.1, basal breadth 0.02.

Habitat.—Central Pacific, Station 271, surface.

9. Heliosestrum ægineta, n. sp.

Disk with spiny surface, four times as broad as the medullary shell. Pores irregular, roundish, of different sizes; twelve to fourteen on the radius. Eight pyramidal marginal spines regularly disposed, four larger (perradial) alternating with four smaller (interradial); the former as long as the radius of the disk, the latter half as long.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the marginal spines 0.05 to 0.1, basal breadth 0.03.

Habitat.—South Atlantic, Station 330, surface.

Subgenus 3. Heliosestomma, Haeckel.

Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

10. Heliosestrum octangulum, n. sp.

Disk with smooth surface, octagonal, twice as broad as the medullary shell. Pores regular, circular; nine to ten on the radius. Equatorial girdle narrow, radially striped, connecting the points of the eight short, regularly disposed, marginal spines in such a manner that the whole shell forms a regular octagon with rectilinear sides.

Dimensions.—Diameter of the disk 0.11 to 0.12, of the medullary shell 0.05 to 0.06; length of the sides of the octagon 0.06.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

11. Heliosestrum octogonium, n. sp.

Disk with smooth surface, octagonal, four times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Equatorial girdle broad, smooth, connecting the points of the eight short, triangular, flat marginal spines in such a manner that the whole shell forms a subregular octagon with concave, nearly equal sides. (Sometimes seven or nine spines instead of eight are developed.)

Dimensions.—Diameter of the disk 0.16 to 0.18, of the medullary shell 0.04 to 0.05; length of the radial spines 0.02 to 0.04, basal breadth 0.03.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

12. Heliosestrum craspedotum, n. sp.

Haliomma humboldti, var., Bury, 1862, Polycystins of Barbados, pl. viii. fig. 4 (below).

Disk with smooth surface, three times as broad as the medullary shell. Pores subregular, circular; ten to twelve on the radius. Eight marginal spines (sometimes seven or nine) triangular, deeply sulcated, half as long and one-third as broad as the radius of the disk, connected by a narrow, radially striped equatorial girdle.

Dimensions.—Diameter of the disk 0.18, of the medullary shell 0.06; length of the radial spines 0.05, basal breadth 0.03.

Habitat.—Central Pacific, Stations 271 to 274, at various depths, also fossil in Barbados.

Genus 192. Astrosestrum,^[18] Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with double medullary shell and with eight radial spines on the margin of the disk (more or less regularly disposed, sometimes seven or nine).

The genus Astrosestrum differs from the foregoing Heliosestrum by the duplication of the medullary shell. The eight marginal spines in the majority of individuals are regularly formed and disposed, of equal size and equidistant. But there are frequent exceptions to this rule, either the angles between the eight spines being more or less different, or the number amounting to seven or nine, instead of eight. Here also in some species four larger (perradial) spines alternate regularly with four smaller (interradial spines), after the same law of symmetry, which is common in the Medusæ.

Subgenus 1. Astrosestantha, Haeckel.

Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines free, not connected by an equatorial girdle.

1. Astrosestrum ephyra, n. sp. (Pl. 32, figs. 4, 4a).

Disk with smooth surface, three times as broad as the outer and nine times as broad as the inner medullary shell. Pores subregular, circular; seven to eight on the radius of the disk. Eight marginal spines (sometimes seven or nine) more or less irregularly disposed, of variable size, commonly as long as the radius of the disk, twice as long as broad, pyramidal, sulcate, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.12, of outer medullary shell 0.04, of the inner 0.014; length of the marginal spines 0.05 to 0.07, basal breadth 0.03.

Habitat.—Central Pacific, Stations 270 to 274, depths 2350 to 2925 fathoms.

2. Astrosestrum nauphanta, n. sp. (Pl. 32, fig. 5).

Disk with smooth surface, two and a half times as broad as the outer and five times as broad as the inner medullary shell. Pores regular, circular; eight to nine on the radius of the disk. Eight marginal spines (often seven or nine) more or less regularly disposed, of equal size, half as long as the radius of the disk, and quite as broad at the base, compressed triangular, sulcate, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.15, of the outer medullary shell 0.06, of the inner 0.03; length of the marginal spines 0.04, basal breadth 0.04.

Habitat.—Pacific, central area, Stations 266 to 268, depth 2700 to 2900 fathoms.

3. Astrosestrum octacanthum, Haeckel.

Haliomma octacanthum, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 295, Taf. viii. fig. 11.

Disk with smooth surface, twice as broad as the outer and six times as broad as the inner medullary shell. Pores regular, circular; six to seven on the radius of the disk. Eight marginal spines regularly disposed, of variable size, the longest as long as the radius, pyramidal, not broader at the base than one pore, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.12, of the outer medullary shell 0.06, inner 0.02; length of the marginal spines 0.03 to 0.06, basal breadth 0.01.

Habitat.—Western Pacific, Philippine Sea, 3300 fathoms, Ehrenberg; Station 225, depth 4475 fathoms.

4. Astrosestrum acraspedum, n. sp.

Disk with smooth surface, three times as broad as the outer and six times as broad as the inner medullary shell. Pores regular, circular; nine to ten on the radius of the disk. Eight marginal spines regularly disposed, of alternating size; four major (perradial) spines as long as the diameter of the disk, four minor (interradial) half as long; spines cylindrical, not broader at the base than one pore, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.035; length of the larger spines 0.2, of the smaller 0.1, basal breadth 0.01.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Subgenus 2. Astrosestilla, Haeckel.

Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines free, not connected by an equatorial girdle.

5. Astrosestrum acanthastrum, n. sp.

Disk with spiny surface, three times as broad as the outer and nine times as broad as the inner medullary shell. Pores subregular, circular; ten to eleven on the radius. Eight marginal spines (sometimes seven or nine) regularly disposed, triangular, about half as long as the radius of the disk, and one-third as broad at the base, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.18, of the outer medullary shell 0.06, of the inner 0.02; length of the radial spines 0.05, basal breadth 0.03.

Habitat.—North Atlantic, Gulf Stream, Færöe Channel, surface, John Murray.

6. Astrosestrum echinastrum, n. sp.

Disk with spiny surface, twice as broad as the outer and four times as broad as the inner medullary shell. Pores irregular, roundish; eight to nine on the radius. Eight marginal spines more or less regularly disposed, pyramidal, nearly as long as the radius of the disk, and not broader at the base than one large pore, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.15, of the outer medullary shell 0.07, of the inner 0.04; length of the radial spines 0.07, basal breadth 0.01.

Habitat.—Fossil in the Tertiary rocks of Sicily, Caltanisetta, Teuscher.

Subgenus 3. Astrosestomma, Haeckel.

Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

7. Astrosestrum pelagia, n. sp.

Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; eight to nine on the radius. Eight marginal spines conical, about as long as the radius of the disk, of nearly equal length, one-third as broad at the base, connected by a radially striped equatorial girdle.

Dimensions.—Diameter of the disk 0.18, of the outer medullary shell 0.06, of the inner 0.023; length of the radial spines 0.09, basal breadth 0.03.

Habitat.—Indian Ocean, Ceylon, Haeckel, surface.

8. Astrosestrum floscula, n. sp.

Disk with smooth surface, two and a half times as broad as the outer and five times as broad as the inner medullary shell. Pores irregular, roundish; ten to eleven on the radius. Eight marginal spines triangular, plain, scarcely half as long as the radius of the disk, nearly as broad at the base, connected by an even equatorial girdle.

Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.08, of the inner 0.04; length of the radial spines 0.09, basal breadth 0.07.

Habitat.—South Atlantic, Station 325, surface.

Subfamily 3. Heliodiscida, Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with a variable number of radial spines on the margin of the disk (ten to twenty or more), which are commonly more or less irregular (sometimes regularly formed and disposed).

Genus 193. Heliodiscus,^[19] Haeckel, 1862, Monogr. d. Radiol., p. 436.

Definition.—Phacodiscida with simple medullary shell and with numerous (ten to twenty or more) simple radial spines on the margin of the disk (commonly with a variable number and an irregular disposition of the undivided spines).

The genus Heliodiscus, the most common and polymorphic of all Phacodiscida, was founded by me in 1862 as the first known type of this family (loc. cit.). I use here the diagnosis of this genus in a restricted sense, including only the species, in which the number of marginal spines amounts to ten, twenty, or more (sometimes fifty to eighty, rarely more than one hundred). The number of spines is in the different species variable, and their disposition commonly more or less irregular, whilst in the preceding genera (with two, three, four, six, or eight marginal spines) their distance and form are commonly regular.

Subgenus 1. Heliodiscetta, Haeckel.

Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

1. Heliodiscus asteriscus, n. sp. (Pl. 33, fig. 8).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; ten to twelve on the radius of the disk. Marginal spines fifteen to twenty, conical, often double contoured, of variable size and disposition, the largest as long as the radius of the disk, as broad at the base as one pore.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the radial spines 0.04 to 0.07, basal breadth 0.01.

Habitat.—Cosmopolitan; Mediterranean (Corfu), Indian Ocean (Madagascar), Atlantic and Pacific, many Stations, surface and various depths.

2. Heliodiscus trochiscus, n. sp. (Pl. 34, figs. 10, 13).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; fourteen to sixteen on the radius. Marginal spines twelve to sixteen, conical, of variable size and disposition, the largest as long as the diameter of the medullary shell, twice as broad as one pore.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.01 to 0.025, basal breadth 0.005.

Habitat.—Central Pacific, Stations 272 to 274, surface.

3. Heliodiscus trigonodon, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; eighteen to twenty on the radius. Marginal spines sixteen to twenty, equilateral triangular, flat, smooth, about as long and broad as the radius of the medullary shell.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.03, basal breadth 0.03.

Habitat.—Central Pacific, Stations 266 to 274, depths 2350 to 2925 fathoms.

4. Heliodiscus glyphodon, n. sp. (Pl. 35, fig. 2).

Heliosestrum glyphodon, Haeckel, 1881, Prodromus et Atlas (pl. xxxv. fig. 2).

Disk with smooth surface, four times as broad as the medullary shell. Pores subregular, circular; seven to eight on the radius. Marginal spines ten to twelve, equilateral triangular, flat, deeply furrowed, twice as long as broad, and as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.14, of the medullary shell 0.035; length of the radial spines 0.07, basal breadth 0.035.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

5. Heliodiscus helianthus, Haeckel.

Haliomma helianthus, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. fig. 1.

Disk with smooth surface, five times as broad as the medullary shell. Pores regular, oblong, disposed regularly in sixty to eighty radial series; fourteen to sixteen on the radius. Marginal spines sixty to eighty, conical, about as long as the diameter of the medullary shell, twice as broad as one pore.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.04; length of the radial spines 0.04, basal breadth 0.005.

Habitat.—Fossil in Barbados.

6. Heliodiscus sol, Haeckel.

Haliomma sol, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 52. Heliodiscus sol, Haeckel, 1862, Monogr. d. Radiol., p. 438.

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; eight to ten on the radius. Marginal spines twenty to thirty, conical, the largest as long as the radius of the medullary shell, their bases widely distant. (The species from Barbados figured by Ehrenberg, 1875, as Haliomma sol, appertains to Heliosestrum solare.)

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.02 to 0.025, basal breadth 0.01.

Habitat.—Fossil in Tertiary rocks of Greece (Ægina), Ehrenberg.

7 Heliodiscus siculus, Stöhr.

Heliodiscus siculus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 89, Taf. i. fig. 14.

Disk with smooth surface, three times as broad as the medullary shell. Pores irregular roundish; seven to eight on the radius. Marginal spines forty to fifty, conical, very irregular, the largest as long as the radius of the medullary shell, their bases coming in contact.

Dimensions.—Diameter of the disk 0.13 to 0.15, of the medullary shell 0.04 to 0.05; length of the radial spines 0.02 to 0.03, basal breadth 0.002 to 0.006.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Teuscher).

8. Heliodiscus polymorphus, n. sp. (Pl. 34, figs. 11, 12).

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius. Marginal spines ten to fifteen, pyramidal, angular, very irregular and variable in size and distribution, the largest nearly as long as the diameter of the disk, as broad at the base as the radius of the medullary shell.

Dimensions.—Diameter of the disk 0.15 to 0.2, of the medullary shell 0.04 to 0.05; length of the radial spines 0.06 to 0.18, basal breadth 0.02 to 0.03.

Habitat.—Central Pacific, Stations 265 to 268, depths 2700 to 2900 fathoms.

9. Heliodiscus solaster, n. sp. (Pl. 34, fig. 4).

Disk with smooth surface, three times as broad as the medullary shell. Pores subregular, roundish; nine to ten on the radius. Marginal spines fifty to sixty, cylindro-conical, flexuose, very variable in size, the largest nearly as long as the diameter of the disk. The spines lie not only in the equatorial plane (as usual), but also in two to four crowded girdles on both sides of it.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the radial spines 0.05 to 0.15, basal breadth 0.008.

Habitat.—Indian Ocean, Madagascar, Rabbe, surface.

Subgenus 2. Heliodiscilla, Haeckel.

Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

10. Heliodiscus phacodiscus, Haeckel.

Heliodiscus phacodiscus, Haeckel, 1862, Monogr. d. Radiol., p. 437, Taf. xvii. figs. 5-7. Haliomma phacodiscus, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 815.

Disk with spiny surface, three times as broad as the medullary shell. Pores regular, circular; six to eight on the radius. Marginal spines twelve to sixteen, conical, as long as the radius of the disk, and one-third as broad as the diameter of the medullary shell.

Dimensions.—Diameter of the disk 0.12 to 0.16, of the medullary shell 0.04 to 0.05; length of the marginal spines 0.06 to 0.08, basal breadth 0.01 to 0.02.

Habitat.—Mediterranean (Messina), Canary Islands (Lanzerote).

11. Heliodiscus amphidiscus, Haeckel.

Heliodiscus amphidiscus, Haeckel, 1862, Monogr. d. Radiol., p. 437. Haliomma amphidiscus, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 154, Taf. ii. figs. 3-7.

Disk with spiny surface, three times as broad as the medullary shell. Pores regular, circular; eight to ten on the radius. Marginal spines twelve to fifteen, bristle-shaped, not larger than the surface spines, about as long as the radius of the medullary shell.

Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.05; length of the marginal spines 0.03, basal breadth 0.002.

Habitat.—Mediterranean (south shore of France), J. Müller.

12. Heliodiscus echiniscus, n. sp. (Pl. 34, fig. 5).

Disk with spiny surface, three times as broad as the medullary shell. Pores irregular, roundish or polygonal; eight to ten on the radius. Marginal spines thirty to fifty, pyramidal, angular, of very variable size, number, and disposition, gradually passing into the surface-spines; the largest nearly as long as the diameter of the medullary shell.

Dimensions.—Diameter of the disk 0.14, of the medullary shell 0.045; length of the radial spines 0.02 to 0.04, basal breadth 0.006.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

13. Heliodiscus pertusus, n. sp. (Pl. 35, fig. 1).

Heliosestrum pertusum, Haeckel, 1881, Prodromus et Atlas (pl. xxxv. fig. 1).

Disk with spiny surface, three times as broad as the medullary shell. Pores irregular, circular, hexagonally framed; eight to ten on the radius. Marginal spines ten to thirty, very variable in size and disposition; commonly eight to twelve larger spines, which are pyramidal, about as long as the radius of the disk and perforated by two to four irregular, longish pores. Between these fenestrated large spines are commonly ten to twenty smaller conical spines, gradually passing into those of the surface.

Dimensions.—Diameter of the disk 0.13 to 0.16, of the medullary shell 0.04 to 0.05; length of the marginal spines 0.04 to 0.08, basal breadth 0.01 to 0.015.

Habitat.—North Pacific, Stations 241 to 244, depths 2300 to 2900 fathoms.

Subgenus 3. Heliodiscomma, Haeckel.

Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

14. Heliodiscus cingillum, n. sp. (Pl. 33, fig. 7).

Disk with smooth surface, five times as broad as the medullary shell. Pores regular, circular; twelve to fourteen on the radius. Equatorial girdle about as broad as the medullary shell, in the proximal half radially striped, on the margin with twenty to twenty-four short, flat, triangular spines, which are shorter than the breadth of the girdle.

Dimensions.—Diameter of the disk 0.25, of the medullary shell 0.05; length of the marginal spines 0.02, basal breadth 0.02.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

15. Heliodiscus humboldti, Haeckel.

Heliodiscus humboldti, Haeckel, 1862, Monogr. d. Radiol., p. 438.

Haliomma humboldti, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 27; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxvii. fig. 3.

Haliomma humboldti, Bury, 1862, Polycystins of Barbados, pl. viii. fig. 3 (at left).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; eighteen to twenty on the radius. Equatorial girdle half as broad as the medullary shell, in the proximal half radially striped, on the margin with sixteen to twenty short, flat, triangular teeth, which are longer than the breadth of the girdle.

Dimensions.—Diameter of the disk 0.12 to 0.2, of the medullary shell 0.03 to 0.05; length of the marginal spines 0.02 to 0.04, basal breadth 0.02.

Habitat.—Fossil in Barbados (common and very variable).

16. Heliodiscus marginatus, n. sp. (Pl. 34, fig. 9).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; nine to ten on the radius. Equatorial girdle one-fourth to one-half as broad as the medullary shell, in the whole breadth radially striped, on the margin with twelve to eighteen very short and broad, triangular, marginal spines.

Dimensions.—Diameter of the disk 0.15 to 0.2, of the medullary shell 0.05 to 0.06; length of the marginal spines 0.01 to 0.02, basal breadth 0.02.

Habitat.—Central Pacific, Stations 265 to 268, depth 2900 fathoms.

17. Heliodiscus sulcatus, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores subregular, circular; twelve to fifteen on the radius. Equatorial girdle as broad as the medullary shell, in the whole breadth radially striped on the margin with ten to fifteen triangular, deeply sulcated teeth, about as long and broad as the medullary shell. (Similar to Heliodiscus glyphodon, Pl. 35, fig. 2, but with broad sulcated girdle and shorter, more numerous spines.)

Dimensions.—Diameter of the disk 0.15 to 0.2, of the medullary shell 0.04 to 0.05; length of the radial spines 0.05 to 0.06, basal breadth 0.04 to 0.05.

Habitat.—Atlantic and Pacific, tropical part, many Stations, surface.

18. Heliodiscus umbonatus, Haeckel.

Haliomma umbonatum, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. fig. 4.

Disk with smooth surface, three times as broad as the medullary shell. Pores irregular, roundish; eight to ten on the radius. Equatorial girdle half as broad as the medullary shell, hyaline, not radially striped, on the margin with ten to twenty triangular, irregular, smooth teeth, very variable in size and disposition.

Dimensions.—Diameter of the disk 0.15 to 0.2, of the medullary shell 0.05 to 0.06; length of the marginal spines 0.02 to 0.08, basal breadth 0.01 to 0.03.

Habitat.—Cosmopolitan; Atlantic, Pacific, in various depths; also fossil in Barbados and Sicily.

Subgenus 4. Heliodiscura, Haeckel.

Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

19. Heliodiscus apollinis, n. sp.

Disk with spiny or bristly surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius. Equatorial girdle narrow, on the margin with sixteen to twenty broad, flat, triangular teeth, which are half as long and one-fourth as broad as the medullary shell. (Very similar to Astrophacus apollinis, Pl. 32, fig. 2, but with simple medullary shell.)

Dimensions.—Diameter of the disk 0.18, of the medullary shell 0.06; length of the marginal spines 0.03, basal breadth 0.015.

Habitat.—Mediterranean (Corfu), Haeckel, surface.

20. Heliodiscus zoroaster, n. sp.

Disk with spiny surface, four times as broad as the medullary shell. Pores subregular, circular; fourteen to sixteen on the radius. Equatorial girdle broad, radially striped, on the margin with ten to twelve pyramidal, deeply sulcated radial spines, which are nearly as long as the radius of the disk, and one-fourth as broad at the base.

Dimensions.—Diameter of the disk 0.24, of the medullary shell 0.06; length of the marginal spines 0.11, basal breadth 0.03.

Habitat.—Indian Ocean, between Aden and Ceylon, Haeckel, surface.

Genus 194. Heliodrymus,^[20] Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with simple medullary shell and with numerous (ten to twenty or more) branched radial spines on the margin of the disk (commonly with a variable number and an irregular disposition of the ramified spines).

The genus Heliodrymus differs from the nearly allied Heliodiscus by the ramification of the marginal spines, a character hitherto observed in no other genus of Phacodiscida. The branching is more or less irregular, either a simple bifurcation or a repeated fissure; the spines and their branches are commonly more or less flexuose. We can distinguish two subgenera: in Heliocladus the surface of the disk is smooth, in Heliodendrum covered with bristle-shaped radial spines, which are either simple or also branched, sometimes longer than the thick marginal spines.

Subgenus 1. Heliocladus, Haeckel, 1881, Prodromus, p. 457.

Definition.—Surface of the disk smooth, without radial spines.

1. Heliodrymus dendrocyclus, n. sp. (Pl. 33, fig. 9).

Heliocladus dendrocyclus, Haeckel, 1881, Prodromus et Atlas (pl. xxxiii. fig. 9).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular, hexagonally framed; eight to nine on the radius. Marginal spines sixteen to twenty, cylindrical, very strong, flexuose, irregularly branched, nearly as long as the diameter of the disk. Between these main spines, each of which bears two to six irregular branches, are scattered on the margin numerous smaller simple spines.

Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.05; length of the main spines 0.1 to 0.14, breadth 0.01 to 0.02.

Habitat.—Central Pacific, Station 271, surface.

2. Heliodrymus furcatus, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius. Marginal spines twenty to twenty-five, cylindrical, flexuose, forked, about as long as the radius of the disk; fork-branches irregular, of unequal size. Some smaller simple spines are scattered between the forked ones.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.04; length of the radial spines 0.07 to 0.09, breadth 0.01.

Habitat.—Central Pacific, Station 265, surface.

3. Heliodrymus grottensis, Haeckel.

Heliodiscus grottensis, Stöhr, 1880, Palæontogr., vol. xxvi. p. 89, Taf. i. fig. 13.

Disk with smooth surface, two and a half times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Marginal spines twenty to thirty, conical, very irregular in form, size, and disposition; the smaller simple, the larger irregularly branched and half as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.17, of the medullary shell 0.07; length of the marginal spines 0.02 to 0.04, basal breadth 0.01 to 0.02.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

Subgenus 2. Heliodendrum, Haeckel.

Definition.—Surface of the disk armed with simple or branched radial spines.

4. Heliodrymus setosus, n. sp.

Disk with spiny surface, four times as broad as the medullary shell. Pores regular, circular; twelve to thirteen on the radius. Marginal spines ten to twelve, cylindrical, irregularly branched, each with two to eight flexuose branches of different sizes; the largest as long as the diameter of the disk. Spines of the surface bristle-shaped, half as long, not branched.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the marginal spines 0.12 to 0.18, breadth 0.025.

Habitat.—North Pacific, Station 254, surface.

5. Heliodrymus ramosus, n. sp. (Pl. 35, figs. 3, 4).

Disk with spiny surface, three times as broad as the medullary shell. Pores regular, circular, hexagonally framed; eleven to twelve on the radius. Marginal spines sixteen to twenty, cylindrical, about as long as the radius, irregularly forked or branched, with unequal flexuose branches. Spines of the surface nearly as long, bristle-shaped, also irregularly branched.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the spines 0.06 to 0.08, basal breadth 0.01 to 0.015.

Habitat.—South Pacific, Station 288, surface.

6. Heliodrymus viminalis, n. sp. (Pl. 35, fig. 5).

Disk with spiny surface, two and a half times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius. Marginal spines fifteen to twenty, cylindro-conical, strong, partly simple, partly forked, about as long as the diameter of the disk. Spines of the surface very numerous, bristle-shaped, longer than the marginal spines, and more branched.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.06; length of the marginal spines 0.11 to 0.14, basal breadth 0.01 to 0.015; length of the surface spines 0.2 to 0.03.

Habitat.—Central Pacific, Station 271, surface.

Genus 195. Astrophacus,^[21] Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with double medullary shell and with numerous (ten to twenty or more) simple radial spines on the margin of the disk (commonly with a variable number and an irregular disposition of the undivided spines).

The genus Astrophacus differs from the similar Heliodiscus in the duplication of the medullary shell. The number and disposition of the radial spines of the margin (commonly between ten and twenty) is also here variable in one and the same species. The greater number of observed species of Astrophacus resemble in a very remarkable manner the corresponding species of Heliodiscus, and differ only in the double medullary shell.

Subgenus 1. Astrophacetta, Haeckel.

Definition.—-Surface of the disk smooth, without radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

1. Astrophacus asteriscus, n. sp.

Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; twelve to fourteen on the radius. Marginal spines fifteen to twenty, of variable size and disposition; the largest as long as the radius of the disk, as broad at the base as one pore. (Very similar to Heliodiscus asteriscus, Pl. 33, fig. 8, but differing in the double medullary shell.)

Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.025; length of the marginal spines 0.05 to 0.1, basal breadth 0.01.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

2. Astrophacus trochiscus, n. sp. (Pl. 34, fig. 14).

Disk with smooth surface, three times as broad as the outer and seven times as broad as the inner medullary shell. Pores irregular, roundish; twelve to thirteen on the radius. Marginal spines sixteen to twenty, conical, of irregular variable size and disposition; the largest as long as the inner medullary shell. (Differs from Heliodiscus trochiscus in the double medullary shell.)

Dimensions.—Diameter of the disk 0.22, of the outer medullary shell 0.08, of the inner 0.03.

Habitat.—North Atlantic, Station 354, surface.

3. Astrophacus solaris, n. sp. (Pl. 32, fig. 1).

Disk with smooth surface, three times as broad as the outer and seven times as broad as the inner medullary shell. Pores subregular, roundish; twelve to fourteen on the radius. Marginal spines one hundred to one hundred and twenty, conical, flexuose, of irregular size and form; the largest one-third as long as the diameter of the disk. The spines lie not only in the equatorial plane (as is usual) but also in two to four crowded girdles on both sides of it. (Very similar to Heliodiscus solaster, Pl. 34, fig. 4, but of double the size, with double the number of spines and with a double medullary shell.)

Dimensions.—-Diameter of the disk 0.3, of the outer medullary shell 0.11, of the inner 0.045; length of the spines 0.03 to 0.1, basal breadth 0.01 to 0.02.

Habitat.—Indian Ocean, Sunda Strait, Rabbe, surface.

Subgenus 2. Astrophacilla, Haeckel.

Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

4. Astrophacus phacodiscus, n. sp. (Pl. 32, fig. 3).

Disk with spiny surface, two and a half times as broad as the outer and seven times as broad as the inner medullary shell. Pores subregular, circular; ten to twelve on the radius. Marginal spines twelve to sixteen, conical, stout, nearly as long as the radius of the disk, and as broad at the base as the inner medullary shell. The numerous bristle-shaped spines of the surface are scarcely half as long. (Similar to Heliodiscus phacodiscus, Haeckel, Monogr. d. Radiol., Taf. xvii. figs. 5-7, but differing in the double medullary shell.)

Dimensions.—Diameter of the disk 0.18, of the outer medullary shell 0.07, of the inner 0.025; length of the marginal spines 0.08 to 0.09, basal breadth 0.03.

Habitat.—South Pacific, Station 300, surface.

Subgenus 3. Astrophacomma, Haeckel.

Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle. (Perhaps = Chilomma(?) Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.)

5. Astrophacus cingillum, n. sp.

Haliomma humboldti, var., Bury, 1862, Polycystins of Barbados, pl. viii. fig. 3 (at right).

Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; eleven to thirteen on the radius. Equatorial girdle about as broad as the inner medullary shell, in the proximal half radially striped, on the margin with eighteen to twenty-four short, flat, triangular spines, about as long as the breadth of the girdle. (Similar to Heliodiscus cingillum, but with double medullary shell.)

Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.025; length of the spines 0.02, basal breadth 0.02.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms; also fossil in Barbados.

6. Astrophacus saturnus, Haeckel.

? Chilomma saturnus, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 297; 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 286, Taf. ii. fig. 5. ? Chilomma saturnus, Haeckel, 1862, Monogr. d. Radiol., p. 447.

Disk with smooth surface, two and a half times as broad as the outer, six times as broad as the inner medullary shell. Pores large, irregular, roundish; five to seven on the radius (?). Equatorial girdle very broad, radially striped, nearly as broad as the outer medullary shell, perforated by twenty to thirty (or more?) radial spines. (The position of this species, and the identity of Chilomma with Astrophacomma, remains doubtful, as the imperfect figure given by Ehrenberg of Chilomma saturnus, the only species of the genus, is in contradiction with his vague description, as is very often the case.)

Dimensions.—Diameter of the disk 0.12 (with girdle 0.22) of the outer medullary shell 0.05, of the inner 0.02.

Habitat.—Arctic Ocean (Greenland, depth 1000 fathoms), Ehrenberg.

Subgenus 4. Astrophacura, Haeckel.

Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

7. Astrophacus apollinis, n. sp. (Pl. 32, fig. 2).

Disk with spiny surface, three times as broad as the outer, eight times as broad as the inner medullary shell. Pores regular, circular; eleven to twelve on the radius of the disk. Equatorial girdle narrow, smooth, on the margin with twelve to sixteen broad, flat, triangular spines, of the same length as the numerous bristle-shaped spines of the surface, which reach half the radius of the disk. (Very similar to Heliodiscus apollinis, but differing in the double medullary shell.)

Dimensions.—Diameter of the disk 0.24, of the outer medullary shell 0.08, of the inner 0.03; length of the radial spines 0.06, basal breadth 0.03.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

Family XX. Coccodiscida, Haeckel (Pls. 36-38).

Coccodiscida, Haeckel, 1862, Monogr. d. Radiol., p. 485.
Coccodiscida, Haeckel, 1881, Prodromus, p. 458.
Lithocyclidina, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad.
⁠d. Wiss. Berlin, p. 214 (partim).

Definition.—Discoidea with extracapsular phacoid shell (or lenticular latticed cortical shell), connected by radial beams with an intracapsular, simple or double, concentric medullary shell, and surrounded by one or more concentric chambered equatorial girdles on the margin.

The family Coccodiscida was founded by me in 1862 for those Discoidea which agree with the Phacodiscida in the formation of the lenticular "phacoid shell" (including a simple or double medullary shell), but differ from them in the development of peculiar concentric chambered rings or girdles around the equatorial margin of the disk, similar to those of the Porodiscida.

The Coccodiscida represent a polymorphic family, in which we here distinguish sixteen genera with fifty-seven species; it comprises the greater part of those Discoidea which Ehrenberg united in his group Lithocyclidina (1875, represented by four genera and eight species); several of these, however, appertain to quite different families, as his Astromma entomocora, Lithocyclia amphitrites, &c. His knowledge of the structure was very imperfect. The peculiar differentiation of the genera and species exhibits the greatest analogy to that of the following family, Porodiscida, though the structure of the central disk in both families is quite different.

The Phacoid Shell, or the circular, lenticular cortical shell exhibits in the Coccodiscida quite the same structure and composition as in the Phacodiscida, described above (p. 420), so that there can be no doubt as to the phylogenetic origin of the former from the latter. Quite in the same way in both families, the lenticular "phacoid shell" is connected by numerous, short, radial beams with the intracapsular, simple or double, medullary shell; and also here these beams are commonly disposed in two groups around the poles of the shortened main axis of the lens, so that their distal ends are implanted in both circumpolar areas (Pl. 36, figs. 2-6; Pl. 37, figs. 3, 7; Pl. 38, figs. 2, 7). The medullary shell is commonly simple, spherical, sometimes a little lenticularly compressed; more rarely it is double, composed of two concentric lattice-shells, which are connected by radial beams; in this case either both concentric medullary shells are spherical, or the inner is spherical, and the outer lenticular, very rarely the inner is lenticular also. In average size and structure they agree perfectly with those of the Phacodiscida.

The Chamber Girdles or "chambered rings" around the equatorial margin of the disk, which constitute the only difference between the Coccodiscida and the Phacodiscida, seem to exhibit a considerable degree of difference of structure in the numerous species of this family; but I regret that I cannot explain them here satisfactorily. The study of these structures is extremely difficult because of the thickness and darkness of the massive opaque shells; to get a perfect knowledge of them, it is indispensable to compare slides made in different directions (horizontal slides through the equatorial and parallel planes, vertical slides through radial and parallel planes, oblique slides in different directions). But this requires a long time and a most careful study of the slides, which are very difficult to get in satisfactory condition. Therefore the following remarks can have only a provisional value.

In all Coccodiscida we can distinguish on the equatorial chamber-girdle of the lens-margin (even on superficial inspection) three different elements of structure, viz.:—(A) concentric circular rings in the equatorial plane; (B) numerous radial beams piercing the former and dividing them into imperfect chambers; (C) porous plates or sieve-plates on both convex faces of the disk. The probable morphological significance of these three elements is the following:—Each ring or girdle corresponds to an outer lenticular cortical shell, which is only developed on the marginal part, whilst its central part is represented by the phacoid shell. Therefore the radial beams (separating the imperfect chambers) are the same as in the concentric Polysphærida, and the sieve-plates of the surface are the porous walls of the cortical shell itself. The correctness of this explanation seems to be proved by such forms as figured in Pl. 38, figs. 2, 4, where the whole surface of the phacoid shell is covered by a concentric chamber-work, as a central continuation of the marginal concentric rings. If we imagine a system of perfect concentric lenticular phacoid shells, compressed strongly from both poles of the shortened main axis, we get the same figure.

Rarely one single girdle only is developed on the equatorial margin of the lenticular disk (Pl. 37, figs. 2, 3, 5). Commonly the number of concentric girdles amounts to three to six, often to ten to twelve or more. Some of these largest Coccodiscida reach a considerable size. Commonly all girdles are of the same breadth, which is about equal to the radius or to the diameter of the inner medullary shell. Rarely the first (or innermost) girdle differs by its greater breadth from the succeeding ones (Pl. 36, fig. 8).

Only in few Coccodiscida the girdle-building remains restricted to the equatorial planes, so that all the chambers lie in it. Commonly on both sides of this plane become developed several layers, and often the number of these (three to six or more) increases towards the periphery; in other cases not their number, but their height increases. Therefore very often the margin of the discoidal shell is much thickened, as thick as the centre of the lenticular phacoid shell (or even more); whilst between the latter and the former (on the proximal girdles) the disk is considerably thinner (Pl. 36, figs. 2, 4; Pl. 37, figs. 7, 8; Pl. 38, figs. 2, 4). The stratified layers communicate by large openings between their chambers. The radial beams are commonly more or less regular and piercing, but also frequently irregular and interrupted; often their number increases towards the margin by intercalation of new beams.

The Pores of the sieve-plates, which cover both sides of the chambered disk, appear on the margin of the phacoid shell as direct continuations of the pores of the latter, and sometimes they are so regularly disposed that one single circular pore is situated on the surface of each chamber (Pl. 36, fig. 7; Pl. 37, fig. 1). But commonly the pores are of variable size and number, two to three on each chamber, and often quite irregularly scattered.

The Margin of the chambered disk exhibits many differences, which afford characters for the distinction of genera. In the first subfamily, the Lithocyclida, the margin is quite simple without radial appendages. In the second subfamily, the Stylocyclida, it is armed with solid radial spines lying in the equatorial plane, and often regularly disposed in the same manner as in the Phacodiscida (compare above, p. 421). In the third subfamily, the Astracturida, the margin bears two or more (commonly three or four) chambered arms, also situated in the plane of the disk, and of the same structure as the circular chambered girdles (Pl. 38). In some cases even the whole system of chamber-girdles is represented only by the radial arms, which are inserted immediately on the margin of the phacoid shell. We may regard therefore these formations as imperfect chambered disks, which are developed only in the direction of certain rays (perradii), and reduced in the direction of the alternating rays (interradii). In some Astracturida the chambered arms exhibit a structure different from the more irregular chamber-work between them, so that we can distinguish the latter, connecting the arms like a web-membrane, as a peculiar "patagium" (as in many Porodiscida) (Pl. 38, figs. 8, 9). Often the distal ends of the chambered arms are armed with a radial spine (Pl. 38, figs. 5, 6, 9).

The Central Capsule of the Coccodiscida is originally always of the same form and shape as in their ancestral group, the Phacodiscida; a circular lenticular disk, which envelops the simple or double medullary shell and is enclosed by the cortical phacoid shell. But whilst in the Phacodiscida the phacoid shell envelops the central capsule perfectly, in the Coccodiscida it envelops only the capsule from the two flat sides (by the upper and lower sieve-plates); the marginal part of the lenticular capsule overgrows the margin of the phacoid shell by peripheral extension, and fills out the chambered cavity of the concentric girdles. In the Lithocyclida and the Stylocyclida, where there are no chambered arms, the central capsule remains a simple circular lens or disk; in the Astracturida, where chambered radial arms surround the margin of the circular central disk, the capsule enters also into these arms and fills out the greatest part of their chambered cavities.

Synopsis of the Genera of Coccodiscida.

I. Subfamily Lithocyclida. Margin of the disk simple, circular, without radial appendages.	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$	Neither radial spines nor chambered arms on the circular margin.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Medullary shell simple,	196. Lithocyclia.
				Medullary shell double,	197. Coccodiscus.
II. Subfamily Stylocyclida. Margin of the disk armed with solid radial spines.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Two opposite spines.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Medullary shell simple,	198. Stylocyclia.
				Medullary shell double,	199. Amphicyclia.
		Three radial spines.		Medullary shell simple,	200. Trigonocyclia.
		Four crossed spines.		Medullary shell simple,	201. Staurocyclia.
		Five to ten or more radial spines.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Medullary shell simple,	202. Astrocyclia.
				Medullary shell double,	203. Coccocyclia.
III. Subfamily Astracturida. Margin of the disk with two to five or more (commonly three or four) hollow radial chambered arms (with or without a connecting patagium). (Medullary shell commonly simple.)	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Two arms, opposite in one axis.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without patagium,	204. Diplactura.
				With patagium,	205. Amphiactura.
		Three radial arms (at equal distances).	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without patagium,	206. Trigonactura.
				With patagium,	207. Hymenactura.
		Four arms (in two crossed diameters).	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without patagium,	208. Astractura.
				With patagium,	209. Stauractura.
		Five radial arms (at variable distances).	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without patagium,	210. Pentactura.
				With patagium,	211. Echinactura.

Subfamily 1. Lithocyclida, Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with simple circular disk, without any radial appendages of the margin (either solid radial spines or chambered arms).

Genus 196. Lithocyclia,^[22] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Coccodiscida with simple circular margin of the disk, without radial appendages. Medullary shell simple.

The genus Lithocyclia is the most simple form of Coccodiscida, and represents the common ancestral form of this family, from which all other genera of it can be derived. The lenticular, biconvex disk is quite simple, composed of a variable number of concentric, circular, chambered rings, which are pierced by radial beams, and which surround the circular lenticular cortical shell or "phacoid shell." The latter contains a simple spherical medullary shell in its centre, and is connected with it by radial beams. The margin of the disk is circular, quite simple, without radial spines or chambered arms.

1. Lithocyclia cingulata, n. sp.

Phacoid shell (or lenticular porous cortical shell) three times as broad as the spherical enclosed medullary shell, surrounded by one single chambered girdle or ring (with about forty chambers of equal size, separated by radial beams). Margin of the disk circular, smooth. Pores of the convex covering plates regular, circular; eight on the radius of the phacoid shell, two on the breadth of the ring.

Dimensions.—Diameter of the disk (with one ring) 0.13, of the phacoid shell 0.1, of the medullary shell 0.033.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

2. Lithocyclia lenticula, n. sp. (Pl. 36, figs. 3, 4).

Phacoid shell two and a half times as broad as the enclosed medullary shell, surrounded by three chambered girdles of equal size, which are divided by piercing radial beams each into about fifty chambers. Margin of the disk thorny. Pores irregular, roundish; seven on the radius of the phacoid shell, two on the breadth of each girdle.

Dimensions.—Diameter of the disk (with three girdles) 0.2, of the phacoid shell 0.11, of the medullary shell 0.045.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

3. Lithocyclia ocellus, Ehrenberg.

Lithocyclia ocellus, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 30; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxix. fig. 3.

Phacoid shell three times as broad as the medullary shell, surrounded by numerous (seven to eleven) chambered rings, which are divided by piercing radial beams each into sixty to ninety chambers. Margin of the disk smooth. Pores regular, circular; nine on the radius of the phacoid shell, one single pore on each chamber.

Dimensions.—Diameter of the disk (with eleven rings) 0.22, of the phacoid shell 0.1, of the medullary shell 0.035.

Habitat.—Fossil in the rocks of Barbados.

4. Lithocyclia monococcus, n. sp.

Stephanopyxis dubiosa (?), Bury, 1862, Polycystins of Barbados, pl. xiii. figs. 1, 2.

Phacoid shell four times as broad as the medullary shell, surrounded by numerous (five to eight) chambered rings, which are divided by piercing radial beams each into fifty to seventy chambers. Margin of the disk thickened, thorny. Pores regular, circular; seven on the radius of the phacoid shell, one single pore on each chamber.

Dimensions.—Diameter of the disk (with eight rings) 0.18, of the phacoid shell 0.12, of the medullary shell 0.03.

Habitat.—Pacific, central area, Station 267, depth 2700 fathoms; also fossil in the rocks of Barbados.

5. Lithocyclia heteropora, n. sp.

Phacoid shell two and a third times as broad as the medullary shell, surrounded by five to nine chambered rings, which are divided by piercing radial beams each into fifty to seventy chambers. Margin of the disk smooth. Pores very different in the inner and outer part of the surface; in the phacoid shell larger, regular, circular, eight on its radius, in the chambered periphery very small and irregular, somewhat spongy.

Dimensions.—Diameter of the disk (with nine rings) 0.2, of the phacoid shell 0.13, of the medullary shell 0.055.

Habitat.—Pacific, central area, Station 263, depth 2650 fathoms.

Genus 197. Coccodiscus,^[23] Haeckel, 1862, Monogr. d. Radiol., p. 485.

Definition.—Coccodiscida with simple circular margin of the disk, without radial appendages. Medullary shell double.

The genus Coccodiscus has quite the same form and structure as the preceding Lithocyclia, and differs from it only in the double medullary shell, composed of two concentric latticed spheres; sometimes the inner medullary shell is spherical, the outer lenticular; the latter is connected with the lenticular phacoid shell (or cortical shell) by radial beams.

1. Coccodiscus lamarckii, n. sp. (Pl. 36, fig. 1).

Phacoid shell (or lenticular porous cortical shell) very thick walled (as thick as one ring), three times as broad as the outer and seven times as broad as the inner medullary shell, surrounded by two to three chambered rings of equal breadth, each of which is divided by piercing radial beams into thirty-six to forty square chambers. Margin of the disk circular, smooth. Pores regular, circular, of equal size; ten on the radius of the phacoid shell, two on the breadth of each chamber.

Dimensions.—Diameter of the disk (with two rings) 0.2, of the phacoid shell 0.14, outer medullary shell 0.05, inner 0.02.

Habitat.—Western Tropical Pacific, Station 220, depth 1100 fathoms.

2. Coccodiscus darwinii, Haeckel.

Coccodiscus darwinii, Haeckel, 1862, Monogr. d. Radiol., p. 486, Taf. xxviii. figs. 11, 12.

Phacoid shell three times as broad as the outer and nine times as broad as the inner medullary shell, surrounded by five to eight chambered rings of equal breadth, each of which is divided by forty piercing radial beams into forty square chambers of equal size. Margin of the disk smooth, circular. Pores irregular, roundish, of unequal size; eleven on the radius of the phacoid shell, one to two on each chamber.

Dimensions.—Diameter of the disk (with eight rings) 0.32, of the phacoid shell 0.11, outer medullary shell 0.036, inner 0.012.

Habitat.—Mediterranean, Messina, surface.

3. Coccodiscus goethei, n. sp. (Pl. 36, fig. 2).

Phacoid shell two and a half times as broad as the outer and five times as broad as the inner medullary shell, surrounded by three to seven chambered rings of equal breadth, each of which is divided by piercing radial beams into sixty to eighty chambers. Margin of the disk thorny. Pores regular, circular; eight on the radius of the phacoid shell, a single one on the breadth of each chamber.

Dimensions.—Diameter of the disk (with seven rings) 0.25, of the phacoid shell 0.1, of the medullary shell 0.04, inner 0.02.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Subfamily 2. Stylocyclida, Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with solid radial spines on the margin of the circular disk, situated in its equatorial plane (without chambered arms).

Genus 198. Stylocyclia,^[24] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Coccodiscida with two opposite solid radial spines on the margin of the circular disk. Medullary shell simple.

The genus Stylocyclia opens the series of the Stylocyclida or of those Coccodiscida in which the margin of the chambered disk is armed with solid radial spines, situated in its equatorial plane, but without chambered arms. Stylocyclia is the most simple form of this subfamily, and bears only two marginal spines, opposite in one equatorial axis of the disk. The medullary shell is simple. This genus corresponds to Xiphodictya in the family Porodiscida. The genus was previously known only by one single species described by Ehrenberg.

1. Stylocyclia dimidiata, Ehrenberg.

Stylocyclia dimidiata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxix. fig. 4.

Phacoid shell three times as broad as the medullary shell, surrounded by five to eight chambered rings of equal breadth, divided by eighty to ninety piercing radial beams into square chambers. Pores subregular, circular; six to seven on the radius of the phacoid shell, a single one on each chamber. Both opposite marginal spines strong, club-shaped, their thickness decreasing from the margin towards the centre of the disk. (The figure of Ehrenberg is very incomplete.)

Dimensions.—Diameter of the disk (with eight rings) 0.25, of the phacoid shell 0.11, of the medullary shell 0.035.

Habitat.—Fossil in the Tertiary rocks of Barbados; living in the depths of the Equatorial Atlantic, Station 348, depth (2450) fathoms.

2. Stylocyclia prionacantha, n. sp. (Pl. 37, fig. 6).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by five to six chambered rings, which are divided by fifty to sixty piercing radial beams into square chambers. Pores in the thick-walled phacoid shell regularly circular, increasing in size from the centre; eight to nine on its radius. Pores on the surface of the chambered girdle smaller, very irregular, two to three on each ring. Both marginal spines longer than the diameter of the disk, with broad serrated edges.

Dimensions.—Diameter of the disk (with five rings) 0.23, of the phacoid shell 0.12, of the medullary 0.05.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

3. Stylocyclia excavata, n. sp. (Pl. 37, fig. 8).

Phacoid shell four times as broad as the medullary shell, surrounded by four chambered rings, which are divided by twenty to thirty radial beams into broad chambers. The height of the rings increases strongly from the centre, so that the fourth ring is two and a half times as high as the first. Pores irregular, roundish; five to six on the radius of the phacoid shell, one to two on the breadth of each ring. Margin of the disk smooth. Both marginal spines thin and long, cylindrical, arising from the medullary shell, longer than the diameter of the disk.

Dimensions.—Diameter of the disk (with four rings) 0.25, of the phacoid shell 0.1, of the medullary shell 0.025.

Habitat.—Fossil in the rocks of Barbados. Indian Ocean, Cocos Islands, Rabbe.

4. Stylocyclia amphacantha, n. sp.

Phacoid shell twice as broad as the medullary shell, surrounded by five chambered rings, divided by piercing beams each into forty to fifty chambers. Pores regular, circular; eight to nine on the radius of the phacoid shell, one on each chamber. Margin of the disk thorny. Both marginal spines strong, conical, as long as its radius.

Dimensions.—Diameter of the disk (with five rings) 0.24, of the phacoid shell 0.1, of the medullary shell 0.05.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Genus 199. Amphicyclia,^[25] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with two opposite solid radial spines on the margin of the circular disk. Medullary shell double.

The genus Amphicyclia has the same form and structure as Stylocyclia, and differs from it only in the double concentric medullary shell. It bears therefore to the latter the same relation that Coccodiscus does to Lithocyclia.

1. Amphicyclia chronometra, n. sp. (Pl. 38, fig. 1).

Phacoid shell three times as broad as the outer and nine times as broad as the inner medullary shell, surrounded by two broad chambered rings, which are divided into irregular chambers by fifty to sixty radial beams of different distance. Margin of the disk thorny, lacerated. Pores irregular, roundish; twelve to sixteen on the radius of the phacoid shell, two to three on the breadth of each ring. The two opposite marginal spines strong, prismatic, with prominent edges, about as long as the diameter of the disk.

Dimensions.—Diameter of the disk (with two rings) 0.24, of the phacoid shell 0.15, outer medullary shell 0.05, inner 0.017.

Habitat.—Pacific, central area, Stations 265 to 268, depths 2700 to 2900 fathoms.

2. Amphicyclia amphistyla, n. sp. (Pl. 37, fig. 7).

Stylocyclia amphistyla, Haeckel, 1879, MS. et Atlas (pl. xxxvii. fig. 7).

Phacoid shell thin walled, two and a half times as broad as the outer and seven times as broad as the inner medullary shell, divided by eighty to ninety radial beams into irregular chambers, which are stratified in four to five floors. Pores regular, circular; eight to nine on the radius of the phacoid shell, two on the breadth of each chamber. Both marginal spines cylindrical.

Dimensions.—Diameter of the disk (with seven rings) 0.27, of the phacoid shell 0.1, outer medullary shell 0.04, inner 0.014.

Habitat.—North Atlantic, Canary Islands, Station 354, surface.

3. Amphicyclia pachydiscus, n. sp. (Pl. 38, fig. 2).

Phacoid shell very thick, spongy, twice as broad as the outer and five times as broad as the inner medullary shell, divided by fifty to seventy radial beams into subregular chambers, which are stratified in five to six floors. Pores irregular, roundish; ten to twelve on the radius of the phacoid shell, two to three on the breadth of each chamber. The two opposite marginal spines quadrangular prismatic, very long, as broad as the radius of the inner medullary shell. Fig. 2 exhibits a vertical section (slide) through the centre.

Dimensions.—Diameter of the disk (with five rings) 0.22, of the phacoid shell 0.1, outer medullary shell 0.05, inner 0.02.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms; fossil in Barbados.

Genus 200. Trigonocyclia,^[26] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with three solid radial spines on the margin of the circular disk. Medullary shell simple.

The genus Trigonocyclia (only known by one single species, once observed) bears on the margin of the chambered disk three solid radial spines, at equal distances one from another. It corresponds to the genus Tripodictya amongst the Porodiscida.

1. Trigonocyclia triangularis, n. sp. (Pl. 37, fig. 5).

Phacoid shell three times as broad as the medullary shell, connected with it by six equidistant radial beams, three of which are prolonged into marginal spines. In the equatorial plane only one single chambered ring, divided by forty-four radial beams into narrow chambers. Pores large, irregular, roundish; five on the radius of the phacoid shell, two on each chamber. Surface and margin of the disk spiny. Three strong conical marginal spines, divergent at equal angles, as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.16, of the phacoid shell 0.12, of the medullary shell 0.04.

Habitat.—Indian Ocean, Zanzibar, depth 2200 fathoms, Pullen.

Genus 201. Staurocyclia,^[27] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with four solid radial spines on the margin of the disk, crossed in two equatorial diameters perpendicular one to another. Medullary shell simple.

The genus Staurocyclia is characterised by four radial spines on the margin of the disk, which are opposite in pairs and situated in two equatorial diameters, commonly perpendicular one to another. They form therefore a rectangular cross (rarely more or less irregular). The genus corresponds exactly to Staurodictya in the family Porodiscida. The medullary shell is simple.

1. Staurocyclia cruciata, n. sp. (Pl. 37, fig. 1).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by six to eight regular rings, which are divided by fifty to seventy piercing beams into square chambers. Pores regular, circular; six on the radius of the phacoid shell, one single pore on each chamber. Four crossed radial spines, arising from the medullary shell by thin bases, prolonged over the dentated margin as four strong quadrangular swords, as long as the radius of the disk.

Dimensions.—Diameter of the disk (with eight rings) 0.23, of the phacoid shell 0.09, of the medullary shell 0.035.

Habitat—Pacific, central area, Station 267, depth 2700 fathoms.

2. Staurocyclia serrata, n. sp.

? Haliomma sp., Bury, 1862, Polycystins of Barbados, pl. xxii. fig. 2.

Phacoid shell twice as broad as the medullary shell, surrounded by three to four spongy rings, which are divided by thirty to forty radial beams into irregular chambers. Pores in the phacoid shell regular, circular, five on its radius; in the chambered spongy girdle much smaller and irregular. Margin dentated, with four crossed, very large, quadrangular spines, as long as the radius of the disk, with wing-shaped, serrated edges.

Dimensions.—Diameter of the disk (with four rings) 0.2, of the phacoid shell 0.1, of the medullary shell 0.05.

Habitat.—Fossil in the rocks of Barbados.

3. Staurocyclia phacostaurus, n. sp. (Pl. 37, figs. 2, 3).

Phacostaurus pyramidalis, Haeckel, 1879, MS. (as a separate genus).

Phacoid shell two and a quarter times as broad as the medullary shell, connected with it by twelve radial beams (four equatorial and eight divergent) and surrounded by one single ring, which is divided by forty radial beams into regular chambers. Pores regular, honeycomb-like in the phacoid shell, seven on its radius; smaller on the equatorial ring, three on its breadth. Four marginal spines pyramidal four-sided, as long and as broad at the base as the ring.

Dimensions.—Diameter of the disk (with one ring) 0.14, of the phacoid shell 0.11, of the medullary shell 0.048.

Habitat.—South Atlantic, Station 335, depth 1425 fathoms.

4. Staurocyclia magniducis, n. sp. (Pl. 37, fig. 4).

Coccostaurus magniducis, Haeckel, 1881, MS. et Atlas (pl. xxxvii. fig. 4).

Phacoid shell twice as broad as the medullary shell, connected with it by numerous radial beams and surrounded by eight chambered rings, which are divided by one hundred to one hundred and twenty piercing radial beams into small chambers. Pores subregular, circular; ten on the radius of the phacoid shell, two on the breadth of each chamber. Margin of the disk armed with numerous bristle-shaped radial spines, as long as the breadth of the chambered girdle. Four very large crossed spines, nearly as long as the diameter of the disk, quadrangular, with four dentated edges; at the club-shaped distal end thorny, as broad as the medullary shell and three times as broad as at the narrow base. I name this splendid species in the honour of H.R.H. the Grand Duke of Saxe-Weimar, Carl Alexander, the magnanimous protector of arts and sciences, the rector magnificentissimus of the University of Jena.

Dimensions.—Diameter of the disk (with eight rings) 0.27, of the phacoid shell 0.11, of the medullary shell 0.05; length of the four crossed club-spines 0.2, basal breadth 0.02, distal breadth 0.06.

Habitat.—Indian Ocean, Ceylon, Belligemma, surface (Haeckel).

Genus 202. Astrocyclia,^[28] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with numerous (five or more, commonly thirty to sixty) solid radial spines on the margin of the circular disk. Medullary shell simple.

The genus Astrocyclia exhibits on the margin of the circular chambered disk a large but variable number of solid radial spines, commonly between thirty and sixty. They are the external prolongations of the inner piercing radial beams, which divide the concentric rings of the disk into chambers. All the spines lie in the equatorial plane of the disk. The genus corresponds to Stylodictya in the family Porodiscida.

1. Astrocyclia solaster, n. sp. (Pl. 36, fig. 7).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by four to six regular rings of equal breadth, which are divided by thirty to forty piercing radial beams into chambers. Pores regular, circular; seven on the radius of the phacoid shell, one single pore on each chamber (the size increasing from the centre). Margin with thirty to forty angular, broad, dentate spines, the prolongations of the inner radial beams.

Dimensions.—Diameter of the disk (with six rings) 0.22, of the phacoid shell 0.1, of the medullary shell 0.04.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

2. Astrocyclia stella, Haeckel.

Lithocyclia stella, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. xxix. fig. 2.

Phacoid shell three times as broad as the medullary shell, surrounded by four to eight rings of increasing breadth from the centre, the outer of which are more or less spongy. Each ring is divided by forty to fifty piercing radial beams into chambers of increasing size. Pores regular, circular; a single one on each chamber, ten on the radius of the phacoid shell. On the margin are scattered ten to twenty thick and short spines, four-sided pyramidal, about as long and as broad at the base as the diameter of the medullary shell.

Dimensions.—Diameter of the disk (with eight rings) 0.25, of the phacoid shell 0.09, of the medullary shell 0.03.

Habitat.—Fossil in the rocks of Barbados.

3. Astrocyclia rotula, n. sp.

Phacoid shell four times as broad as the medullary shell, surrounded by one single ring, which is divided by forty radial beams into equal chambers. Pores regular, circular; two on the breadth of the ring, six on the radius of the phacoid shell. Margin with forty short, conical spines, the prolongations of the inner radial beams, twice as long as the breadth of the ring.

Dimensions.—Diameter of the disk 0.13, of the phacoid shell 0.1, of the medullary shell 0.025.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

4. Astrocyclia arachnia, n. sp.

Phacoid shell twice as broad as the medullary shell, surrounded by four to six rings of equal breadth, which are divided by twelve to twenty radial beams into broad chambers. Pores regular, circular; two on the breadth of each ring, eight on the radius of the phacoid shell. Margin with twelve to twenty very long and thin, bristle-shaped, radial spines, the prolongations of the inner beams, longer than the diameter of the disk. (Resembles Stylodictya arachnia, but differs in the possession of a phacoid shell.)

Dimensions.—Diameter of the disk (with six rings) 0.22, of the phacoid shell 0.09, of the medullary shell 0.045.

Habitat.—North Atlantic, Canary Islands.

5. Astrocyclia heterocycla, n. sp. (Pl. 36, fig. 8). Phacoid shell two and a half times as broad as the medullary shell, surrounded by three rings of unequal breadth, the first ring as broad as the second and third together. They are divided by fifty to sixty piercing radial beams into chambers, which are square in the second and third rings, and half as large as in the first. The radial beams are alternately thicker and thinner, prolonged into short marginal spines. Pores subregular, circular; eight on the radius of the phacoid shell, two on the breadth of the first ring, a single one on each chamber of the second and third rings.

Dimensions.—Diameter of the disk (with three rings) 0.2, of the phacoid shell 0.12, of the medullary shell 0.05.

Habitat.—Equatorial Atlantic, Station 348, depth (2450) fathoms; also fossil in Barbados.

Genus 203. Coccocyclia,^[29] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with numerous (five or more) solid radial spines on the margin of the circular disk. Medullary shell double.

The genus Coccocyclia has the same form and structure as the foregoing Astrocyclia, and differs from it only in the double concentric medullary shell. It bears therefore to the latter the same relation as Coccodiscus to Lithocyclia.

1. Coccocyclia liriantha, n. sp.

Phacoid shell three times as broad as the outer and ten times as broad as the inner medullary shell, connected with both by six equidistant piercing radial beams. The margin of the phacoid shell is surrounded by one or two equatorial rings, each as broad as the outer medullary shell, and divided by thirty to forty radial beams into narrow chambers. Pores subregular, circular, about nine to ten on the radius of the phacoid shell, three to four on the breadth of each ring. Margin of the disk ciliated, with six regularly disposed radial spines as prolongations of the inner six piercing beams. Each spine cylindrical, delicately crenulated, about as broad as the inner medullary shell, and once to twice as long as the diameter of the whole disk, elegantly undulated, with a conical terminal point.

Dimensions.—Diameter of the disk (with two rings) 0.32, of the phacoid shell 0.2, of the outer medullary shell 0.06, of the inner 0.02.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

2. Coccocyclia heliantha, n. sp. (Pl. 36, figs. 5, 6).

Phacoid shell two and a half times as broad as the outer and six times as broad as the inner medullary shell, surrounded by six to eight rings of nearly equal breadth, the outer somewhat smaller. They are divided by fifty to sixty piercing radial beams into irregular chambers. Pores irregular, roundish; ten on the radius of the phacoid shell, a single one on each chamber of the equatorial girdle. Margin of the disk with numerous strong conical radial spines of different breadths, arranged in several circles, the strongest in the equatorial plane, about as broad as one ring and twice as long. Surface thorny.

Dimensions.—Diameter of the disk (with seven rings) 0.3, of the phacoid shell 0.12, of the outer medullary shell 0.05, of the inner 0.02.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms; also fossil in Barbados.

Subfamily 3. Astracturida, Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with two or more (commonly three or four) chambered radial arms on the margin of the disk, situated in its equatorial plane (with or without a connecting patagium between the arms).

Genus 204. Diplactura,^[30] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with two opposite chambered arms on the margin of the circular disk, without a connecting patagium.

The genus Diplactura is the simplest form of the Astracturida, or of those Coccodiscida in which the margin of the disk bears chambered arms, situated in its equatorial plane. This subfamily corresponds to the Euchitonida among the Porodiscida, to the Spongobrachida among the Spongodiscida. In Diplactura there are only two free arms, opposite in one equatorial diameter (corresponding to Amphibrachium among the former, to Spongolena among the latter).

Subgenus 1. Diplacturium, Haeckel.

Definition.—Arms blunt at the distal end, without radial spines.

1. Diplactura diplobrachia, n. sp.

Phacoid shell twice as broad as the medullary shell, with six pores on its radius, without a perfect chambered ring around it. Arms club-shaped, one and a half times as long as the diameter of the phacoid shell, at the distal end rounded, blunt, as broad as the latter, at the base only half as broad.

Dimensions.—Diameter of the phacoid shell 0.08, of the medullary shell 0.04; length of the arms 0.12, basal breadth 0.04, distal breadth 0.08.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Subgenus 2. Diplactinium, Haeckel.

Definition.—Arms on the distal end armed with a radial terminal spine.

2. Diplactura diploconus, n. sp. (Pl. 38, fig. 5).

Amphiactura diploconus, Haeckel, 1877, MS. et Atlas (pl. xxxviii. fig. 5).

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius, surrounded by a single chambered ring. Arms club-shaped, twice as long as the diameter of the phacoid shell, at the distal end as broad as the latter, at the base only half as broad. Both poles of the common axis of the arms are armed with a strong spindle-shaped terminal spine.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms (without terminal spines) 0.17, basal breadth 0.05, distal breadth 0.09.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

Genus 205. Amphiactura,^[31] Haeckel, 1881, Prodromus, p. 458.

Definition.—Coccodiscida with two opposite chambered arms on the margin of the circular disk, connected by a spongy patagium.

The genus Amphiactura differs from the foregoing Diplactura in the development of a patagium between the arms, and therefore bears the same relation to it as Amphymenium in the Porodiscida does to Amphibrachium, or Spongobrachium in the Spongodiscida does to Spongolene. In this and in the following Discoidea provided with a patagium, this connecting web constantly exhibits a different texture of its framework, which is sometimes more regularly chambered, at other times more irregularly spongy.

1. Amphiactura amphibrachia, n. sp. (Pl. 38, figs. 3, 4).

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius. Arms nearly equilateral triangular, twice as long as the diameter of the phacoid shell, at the truncated distal end as broad as the latter, at the base only one-third as broad. Patagium a circular lenticular disk, enveloping only the basal third of the arms, with three to four concentric circular rings, divided into chambers by about forty radial beams, which are prolonged beyond the margin of the patagium into radial spines. The vertical section (fig. 4) shows that the chambers of each arm (eleven to twelve transverse rows in the radius) are disposed in two layers.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.18, basal breadth 0.03, distal breadth 0.09.

Habitat.—Pacific, central area, Station 263, depth 2650 fathoms.

Genus 206. Trigonactura,^[32] Haeckel, 1881, Prodromus, p. 459.

Definition.—Coccodiscida with three chambered arms on the margin of the circular or triangular disk, without a connecting patagium.

The genus Trigonactura exhibits three radial arms, which in all known species are separated by three equal angles. The terminal points of the arm-axes are the corners of an equilateral triangle. It corresponds therefore to Dictyastrum among the Porodiscida.

Subgenus 1. Trigonacturium, Haeckel.

Definition.—Distal end of the arms blunt or truncated, without a terminal spine.

1. Trigonactura pythagoræ, Haeckel.

Astromma pythagoræ, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xxx. fig. 2.

Phacoid shell circular, twice as broad as the medullary shell, with five pores on its radius, without a completely surrounding chambered girdle. Arms nearly square, at the truncated distal end as broad as long, and scarcely broader than at the base, two-thirds as long as the diameter of the central disk.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.07, distal breadth 0.07.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, in various depths; also fossil in Tertiary rocks of Barbados and Nicobar.

2. Trigonactura rhopalastrella, n. sp.

Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pl. xv. fig. 7.

Phacoid shell twice as broad as the medullary shell, with five pores on its radius, without a perfect chambered ring around it. Arms club-shaped, at the blunt distal end rounded, as long as the diameter of the phacoid shell; their basal breadth is one-fourth, their distal breadth one-half of its length.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.1, basal breadth 0.025, distal breadth 0.05.

Habitat.—Pacific, central area, Stations 270 to 274, depths 2400 to 2800 fathoms; also fossil in Tertiary rocks of Barbados.

3. Trigonactura trigonobrachia, n. sp.

Phacoid shell two and a half times as broad as the medullary shell, with six pores on its radius, without a perfect chambered girdle. Arms nearly equilateral triangular, twice as long as the diameter of the phacoid shell, at the truncated distal end as broad as its diameter and three times as broad as at the narrow base. (Resembles Hymenactura hexagona, but without a patagium.)

Dimensions.—Diameter of the phacoid shell 0.11, of the medullary shell 0.045; length of the arms 0.2, basal breadth 0.035, distal breadth 0.1.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

4. Trigonactura lanceolata, n. sp.

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius, surrounded by one perfect chambered ring. Arms lanceolate, three times as long as the diameter of the phacoid shell, and four times as long as broad in the middle part, at both ends very narrow, blunt.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.25, breadth in the midst 0.06.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Subgenus 2. Trigonactinium, Haeckel.

Definition.—Distal end of the arms armed with a radial spine.

5. Trigonactura triacantha, n. sp. (Pl. 38, figs. 6, 7).

Phacoid shell two and a half times as broad as the medullary shell, with eight pores on its radius, surrounded by one perfect chambered ring. Arms nearly lanceolate, in the middle part one and a half times as broad as at both ends, twice as long as the phacoid shell, at the distal end with a strong pyramidal terminal spine. Through the spongy framework of each arm shine sixteen to eighteen transverse bars (as septa of the joints) and six to eight longitudinal piercing beams.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.038; length of the arms 0.2, greatest breadth 0.08.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

6. Trigonactura trigonodiscus, n. sp.

? Astromma sp., Bury, 1862, Polycystins of Barbados, Taf. xv. fig. 2.

Phacoid shell triangular, twice as broad as the spherical medullary shell, with six to seven pores on its radius, surrounded by one chambered ring. Arms equilateral triangular, as long as the diameter of the central disk and at the base half as broad, slowly decreasing in breadth towards the distal end, which is armed with a strong pyramidal spine.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.12, basal breadth 0.07.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms; also fossil in Barbados.

7. Trigonactura trixiphos, n. sp.

Phacoid shell circular, twice as broad as the medullary shell, without a completely surrounding chambered ring, with four pores on its radius. Arms club-shaped, about as long as the diameter of the central disk, at the base half as broad as long, at the rounded distal end broader, and armed with a strong pyramidal terminal spine, nearly as long as the arm itself.

Dimensions.—Diameter of the phacoid shell 0.08, of the medullary shell 0.04; length of the arms (without terminal spine) 0.08, basal breadth 0.04, distal breadth 0.06.

Habitat.—Fossil in the rocks of Barbados.

Genus 207. Hymenactura,^[33] Haeckel, 1881, Prodromus, p. 459.

Definition.—Coccodiscida with three chambered arms on the margin of the circular or triangular disk, connected by a spongy patagium.

The genus Hymenactura differs from the foregoing Trigonactura in the spongy patagium between the arms, and bears therefore to it the same relation that among the Porodiscida Hymeniastrum does to the simpler Dictyastrum. The oldest known species of this genus is Hymenactura pythagoræ, described by Ehrenberg as Hymeniastrum pythagoræ, but differing from this in the structure of the central disk.

Subgenus 1. Hymenacturium, Haeckel.

Definition.—Distal end of the arms blunt or truncated, without terminal spines.

1. Hymenactura archimedis, n. sp. (Pl. 38, fig. 8).

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius. Arms nearly trapezoidal, somewhat longer than the diameter of the central disk, at the truncated distal end nearly as broad, at the base only half as broad. In each arm eleven to twelve transverse rows of square chambers, each of which exhibits on the surface one large pore. Patagium enveloping the basal half of the arms, with four to five convex rows of chambers, forming together a circular concentric disk.

Dimensions.—Diameter of the phacoid shell 0.11, of the medullary shell 0.035; length of the arms 0.12, basal breadth 0.05, distal breadth 0.1.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

2. Hymenactura pythagoræ, Haeckel.

Hymeniastrum pythagoræ, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 31; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 76, Taf. xxx. fig. 5.

Phacoid shell three times as broad as the medullary shell, with six pores on its radius. Arms nearly trapezoidal, somewhat longer than the diameter of the central disk, at the truncated distal end nearly as broad, at the base two-thirds as broad. In each arm eight to nine transverse rows of square chambers, each chamber with one pore on the surface. Patagium enveloping the basal half of the arms, with four to five rectilinear parallel rows of chambers, forming together a regular triangle. Differs from the preceding species mainly in the quite different structure of the patagium, from the true Hymeniastrum pythagoræ in the phacoid shell of the central disk, which encloses only one simple medullary shell.

Dimensions.—Diameter of the phacoid shell 0.11, of the medullary shell 0.04; length of the arms 0.13, basal breadth 0.07, distal breadth 0.12.

Habitat.—Fossil in the rocks of Barbados.

3. Hymenactura trigona, n. sp.

Astromma sp., Bury, 1862, Polycystins of Barbados, pl. xv. fig. 1.

Phacoid shell twice as broad as the medullary shell, with four to five pores on its radius. Arms slender, lanceolate, three times as long as the diameter of the phacoid shell and five times as long as broad in the middle part; distal ends blunt. Patagium enveloping only the basal half of the arms, forming a regular triangle with concave sides.

Dimensions.—Diameter of the phacoid shell 0.08, of the medullary shell 0.035; length of the arms 0.2, greatest breadth 0.04.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms; fossil in the rocks of Barbados.

4. Hymenactura hexagona.

Hymeniastrum sp., Bury, 1862, Polycystins of Barbados, pl. xv. fig. 3.

Phacoid shell twice as broad as the medullary shell, with four to five pores on its radius. Arms nearly equilateral triangular, three times as long as the diameter of the phacoid shell, at the truncated distal end nearly three-fourths as broad as long, at the narrow base only one-fourth as broad. Patagium complete, enveloping the arms completely, so that the whole body represents a regular hexagonal disk.

Dimensions.—Diameter of the phacoid shell 0.08, of the medullary shell 0.04; length of the arms 0.18, basal breadth 0.04, distal breadth 0.16.

Habitat.—Fossil in the rocks of Barbados and Nicobar.

Subgenus 2. Hymenactinium, Haeckel.

Definition.—Distal ends of the arms armed with terminal spines.

5. Hymenactura ptolemæi, n. sp.

Astromma sp., Bury, 1862, Polycystins of Barbados, pl. xv. figs. 5, 6.

Phacoid shell twice as broad as the medullary shell, with six to seven pores on its radius. Arms nearly square, about as large as the phacoid shell, at the truncated distal end little broader than at the base, and armed with a strong pyramidal terminal spine. Patagium incomplete, enveloping the basal half of the arms.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length and greatest breadth of the arms 0.08.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms; fossil in the rocks of Barbados.

6. Hymenactura copernici, n. sp. (Pl. 38, fig. 9).

Phacoid shell three times as broad as the medullary shell, with six pores on its radius. Arms lanceolate, nearly twice as long as the phacoid shell, in the middle part twice as broad as the medullary shell, with a strong conical terminal spine at the distal end. In each arm about ten transverse rows of chambers. Patagium enveloping the basal half of the arms, with four convex parallel rows of chambers.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.035; length of the arms 0.17, greatest breadth 0.07.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

Genus 208. Astractura,^[34] Haeckel, 1881, Prodromus, p. 459.

Definition.—Coccodiscida with four chambered arms on the margin of the circular or quadrangular disk, crossed in two equatorial diameters, without a connecting patagium.

The genus Astractura has the form of a regular cross, four radial arms being opposite in two equatorial diameters perpendicular one to another. In the Porodiscida the same form is repeated by Stauralastrum, in the Spongodiscida by Spongasteriscus. The oldest known species of the genus is Astromma aristotelis of Ehrenberg, in which genus this author confounded triradial and four-radial forms.

Subgenus 1. Astracturium, Haeckel.

Definition.—Distal end of the arms blunt or truncated, without terminal spines.

1. Astractura ordinata, n. sp.

? Astromma sp., Bury, 1862, Polycystins of Barbados, pl. xiv. fig. 3.

Phacoid shell three times as broad as the medullary shell, with six pores on its radius, without a completely developed chambered ring. Arms trapezoidal, somewhat longer than the radius of the disk, at the truncated distal end as broad as long, at the base one-third smaller.

Dimensions.—Diameter of the phacoid shell 0.08, of the medullary shell 0.03; length of the arms 0.05, distal breadth 0.05, basal breadth 0.035.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms; also fossil in Barbados.

2. Astractura clavigera, n. sp.

Astromma aristotelis, Bury, 1862, Polycystins of Barbados, pl. iv. fig. 2.

Phacoid shell twice as broad as the medullary shell, with ten pores on its radius, surrounded by one perfect chambered ring. Arms club-shaped, about as long as the radius of the central disk, at the rounded distal end two-thirds, at the base one-third as broad as long.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.06, basal breadth 0.02, distal breadth 0.04.

Habitat.—Pacific, central area, Stations 270 to 274, depths 2350 to 2925 fathoms; fossil in the rocks of Barbados.

Subgenus 2. Astractinium, Haeckel.

Definition.—Distal end of the arms furnished with a radial spine.

3. Astractura aristotelis, Haeckel.

Astromma aristotelis, Ehrenberg, 1856, Microgeol., Taf. xxxvi. fig. 32; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 66, Taf. xxx. fig. 4.

Astromma aristotelis, Haeckel, 1862, Monogr. d. Radiol., p. 489.

? Astromma aristotelis, Bury, 1862, Polycystins of Barbados, pl. xiv. fig. 4.

Phacoid shell three times as broad as the medullary shell, with six to eight pores on its radius, surrounded by one perfect chambered ring. Arms nearly trapezoidal, about as long as the diameter of the central disk, at the base half as broad, at the truncated distal end nearly as broad as long, and armed with a large pyramidal terminal spine. Each arm with about eight transverse and longitudinal rows of chambers.

Dimensions.—Diameter of the phacoid shell 0.11, of the medullary shell 0.04; length of the arms 0.1, basal breadth 0.05, distal breadth 0.09.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, at various depths; fossil in the Tertiary rocks of Barbados and Nicobar.

4. Astractura democriti, n. sp.

Astromma aristotelis, var., Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf, xxx. fig. 3. ? Astromma aristotelis, var., Bury, 1862, Polycystins of Barbados, pl. xiv. fig. 4.

Phacoid shell twice as broad as the medullary shell, with five to seven pores on its radius, without perfect chambered ring. Arms about twice as long as broad, longer than the diameter of the central disk, at the truncated distal end a little broader than at the base, and armed with a strong, pyramidal, terminal spine.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.15, basal breadth 0.04, distal breadth 0.08.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms; fossil in Barbados.

5. Astractura hippocratis, n. sp.

Phacoid shell three times as broad as the medullary shell, with seven pores on its radius, surrounded by two to three perfect chambered rings. Arms nearly square, scarcely as long and nearly as broad as the diameter of the central disk, at the rounded distal end armed with a very strong, pyramidal, terminal spine, longer than the arm itself, and at the base as broad as the medullary shell.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.08, breadth 0.1.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Genus 209. Stauractura,^[35] Haeckel, 1881, Prodromus, p. 459.

Definition.—-Coccodiscida with four chambered arms on the margin of the circular or quadrangular disk, crossed in two equatorial diameters, connected by a spongy patagium.

The genus Stauractura differs from the foregoing in the patagium between the arms, and bears therefore the same relation to it as Histiastrum in the Porodiscida does to Stauralastrum. All known species of this genus form a regular square, if we connect the end points of the arm axes by lines.

Subgenus 1. Stauracturium, Haeckel.

Definition.—Distal end of the arms blunt or truncated, without terminal spines.

1. Stauractura octogona, n. sp.

Phacoid shell twice as broad as the medullary shell, with eight pores in its radius. Arms nearly square, little larger than the phacoid shell, with broad truncated distal ends. The corners of the latter are so connected by the complete patagium, that the whole shell forms a regular octagon.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.12, distal breadth 0.11.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

2. Stauractura tetragona, n. sp.

Phacoid shell three times as broad as the medullary shell, with eleven pores on its radius. Arms club-shaped, nearly as long as the diameter of the phacoid shell, and one and a half times as long as broad at the distal part; at the distal end rounded, blunt, without terminal spine. The terminal points of the arms are so connected by a thin, complete patagium, that the whole shell becomes a regular square.

Dimensions.—Diameter of the phacoid shell 0.13, of the medullary shell 0.045; length of the arms 0.12, greatest breadth 0.08.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Subgenus 2. Stauractinium, Haeckel.

Definition.—Distal end of the arms furnished with a radial spine.

3. Stauractura medusina, n. sp.

Phacoid shell two and a half times as broad as the medullary shell, with nine pores on its radius. Arms club-shaped, one and a half times as long as the diameter of the phacoid shell, and in the outer third nearly as broad as the latter, at the base scarcely one-third as broad; their truncated distal end armed with a strong pyramidal terminal spine. Patagium incomplete, enveloping only the basal half of the arms, with three rectilinear parallel rows of chambers, forming a square.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.04; length of the arms 0.14, greatest breadth 0.08.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

4. Stauractura quadrata, n. sp.

Phacoid shell twice as broad as the medullary shell, with seven pores on the radius. Arms nearly square, about as large as the phacoid shell, with a strong pyramidal terminal spine at the distal end. Patagium complete, between every two arms triangular, with rectilinear parallel rows of chambers; it connects the end points of the arm radius in such a manner that the whole shell becomes a regular square.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.045; length of the arms 0.1, greatest breadth 0.08.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

Genus 210. Pentactura,^[36] Haeckel, 1881, Prodromus, p. 459.

Definition.—Coccodiscida with five chambered arms on the margin of the circular or pentagonal disk, without a connecting patagium.

The genus Pentactura possesses five free radial arms, and resembles Pentalastrum among the Porodiscida. The distance of the five arms seems to be sometimes equal, at other times different in one and the same species.

1. Pentactura pentactis, Haeckel.

Astromma pentactis, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xxx. fig. 1.

Phacoid shell two and a half times as broad as the medullary shell, with eight pores on its radius. Arms regularly or irregularly disposed, nearly square, about half as large as the phacoid shell, at the truncated distal end little broader than at the base. In the specimen figured, and very imperfectly described by Ehrenberg, (loc. cit.), the arms were asymmetrically disposed, two opposite in one axis of the disk, two others on one side of this axis, the fifth opposite to these on the other side. Another specimen which I found in the Barbados rocks had five arms of equal size, regularly disposed, at equal intervals.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.04; length and breadth of the arms 0.05 to 0.06.

Habitat.—Fossil in the rocks of Barbados.

2. Pentactura astropecten, n. sp.

Phacoid shell three times as broad as the medullary shell, with ten pores on its radius. Arms regularly disposed, club-shaped, nearly twice as long as the diameter of the phacoid shell, and equal to it in breadth at the rounded distal end. The latter is armed with a short conical spine, and is twice as broad as the base.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.17, basal breadth 0.05, distal breadth 0.08.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Genus 211. Echinactura,^[37] n. gen.

Definition.—Coccodiscida with five chambered arms on the margin of the circular or pentagonal disk, connected by a spongy patagium.

The genus Echinactura differs from the foregoing Pentactura in the patagium between the arms, and bears therefore the same relation to it as Pentinastrum in the Porodiscida does to Pentalastrum.

1. Echinactura culcita, n. sp.

Phacoid shell pentagonal, three times as broad as the medullary shell, with nine pores on its radius. Arms egg-shaped, about as long as the diameter of the phacoid shell, and in the distal part half as broad. The blunt ends of the arms are so connected by the complete patagium that the whole shell becomes a regular pentagonal disk.

Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.035; length of the arms 0.11, basal breadth 0.04, distal breadth 0.06.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

2. Echinactura asteriscus, n. sp.

Phacoid shell twice as broad as the medullary shell, with seven pores on its radius. Arms lanceolate, twice as long as the diameter of the phacoid shell, in the middle part nearly as broad as the latter, at the distal end with a strong conical terminal spine. Patagium incomplete, enveloping only the basal half of the arms.

Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.045; length of the arms 0.2, greatest breadth 0.08.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

3. Echinactura goniaster, n. sp.

Phacoid shell three times as broad as the medullary shell, with nine pores on its radius. Arms club-shaped, one and a half times as long as the diameter of the phacoid shell, in the distal part nearly as broad as the latter, in the basal part one-third as broad; at the end a strong pyramidal spine. Patagium nearly complete, with concave dentated margin between each pair of arms, therefore the pentagonal disk of the whole shell with concave sides.

Dimensions.—Diameter of the phacoid shell 0.12, of the medullary shell 0.04; length of the arms (without terminal spine) 0.18, basal breadth 0.04, distal breadth 0.1.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Family XXI. Porodiscida, Haeckel (Pls. 41-47).

Porodiscida, Haeckel, 1881, Prodromus, p. 459.
Trematodiscida et Discospirida, Haeckel, 1862, Monogr. d. Radiol.,
⁠pp. 485, 491, 513.
Calodictya, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss.
⁠Berlin, p. 53 (partim).

Definition.—Discoidea without phacoid shell, with flat discoidal shell, in which a simple spherical central chamber is surrounded by concentric chambered rings (each ring divided by radial beams into imperfect chambers). Surface of the disk on the two flat sides covered by a porous sieve-plate.

The family Porodiscida is by far the largest and richest in different and common forms among all Discoidea; already in my Monograph (1862) nine genera and twenty-eight species have been enumerated. Their number is here increased to more than thirty genera and two hundred species. Many of these species appertain to the most common and widely distributed Spumellaria, both living and fossil. But the study of their structure is not easy, and requires (as in the foregoing Coccodiscida) not only careful examination of the facial views of the disk, but also of the marginal view and of slides and sections through different planes.

In my Monograph (1862, pp. 485, 491, 513) I had constituted for these Discoidea two different families, the Trematodiscida and Discospirida; but the comparative study of a far greater number of different types in the Challenger collection has since convinced me that those two families are but little different, and united by transitional forms within one and the same genus, so that they must be united as Porodiscida. Of the group, which Ehrenberg formerly had called "Calodictya," many genera appertain to the Porodiscida, whilst many others are true Spongodiscida.

The Porodiscida represent the first and the most important family of the Cyclodiscaria, or of those Discoidea which are devoid of the peculiar extracapsular lenticular "phacoid shell," characteristic of the three preceding families (united therefore as Phacodiscaria). Probably all Cyclodiscaria can be derived from Archidiscus, from a morphological as well as a phylogenetic point of view. Archidiscus seems to be the common ancestral form not only of the Porodiscida, but also of the nearly allied Pylodiscida and Spongodiscida. This important Archidiscus (Pl. 48, figs. 9-11) is a small lenticular circular disk, in which a simple latticed spherical central chamber is surrounded by one single concentric ring, connected with it by a variable number of radial beams in the equatorial plane. From this typical Archidiscus, as from their "architype," all other Cyclodiscaria may be derived; the Porodiscida by regular apposition of new concentric chambered rings on the margin, the Spongodiscida by irregular apposition of a spongy framework, the Pylodiscida by a peculiar interrupted, concentric, triradial growth, three radial arm-chambers alternating with three open gates or holes, so that already the first chambered ring is not complete.

Archidiscus (Pl. 48, figs. 9-11) is not only the common phylogenetic ancestral form of all Cyclodiscaria, but also the common ontogenetic original form of all Porodiscida, or at least of the greater part of them. The numerous species of Archidiscus, which are distinguished in the sequel, are at the same time the embryonic forms of different Porodiscida, corresponding to the "biogenetic main law of development." The small shell of Archidiscus is sometimes completely lenticular, circular, at other times more or less polygonal; commonly on the biconvex centre much thicker than on the margin, but sometimes also of nearly equal thickness (like a medal or a short cylinder). The latticed central chamber of it is probably in the majority of species spherical, but in some more or less compressed, lenticular; the number of small pores on its surface is probably commonly between ten and twenty (four to eight usually being visible on each hemisphere). The number of radial beams, which connect it with the equatorial ring, varies commonly from four to eight; but sometimes only two or three are to be found, in other cases nine to ten or more. The regular disposition of these beams (in certain equatorial axes of the disk) is probably of great importance, as determining the later development of characteristic radial appendages of the margin in the more highly developed Porodiscida. The equatorial ring itself, forming the margin of the lenticular disk, is either a simple solid ring or a broader latticed girdle; in the latter case it merges slowly into the opposite sieve-plates of the two flat disk sides, or the porous "cover-plates," covering its parallel or convex surfaces. These latter can be regarded as direct peripheral continuations of the polar regions of the spherical central chamber. The ring-chambers, surrounding the latter in a single circle, are commonly of nearly the same breadth, but often also of different irregular size. Their number varies between two and ten or more, but commonly between four and eight; each ring-chamber is covered on the upper and lower side by the sieve-plate, bounded on the inner (proximal) side by the wall of the central chamber, on the outer (distal) side by the marginal ring, on both lateral sides by the contiguous neighbouring ring-chambers.

The important question as to the phylogenetic origin of Archidiscus can be answered in a twofold way. The most simple form of Archidiscus (Archidiscus dioniscus) can be derived immediately from the Stylosphærida, Saturnalis (Pl. 13, fig. 16), only by the development of lattice-work between the equatorial ring and the two polar faces of the concentric central chamber (on the surface of the biconvex jelly-mantle). But on the other hand Archidiscus may also be derived from the simplest Phacodiscida, Sethodiscus (Pl. 33, figs. 1-3), by the stronger compression of the biconvex lenticular shell, so that the enclosed medullary shell on the two poles runs together with the lenticular phacoid shell, of which only the peripheral part remains free, and thus forms the chambered ring; this latter explanation seems the more natural in many cases, as often in the Porodiscida the central chamber is enclosed in one or two concentric spherical or lenticular lattice-shells.

The second subfamily of the Porodiscida are the Trematodiscida, which are derived from the preceding Archidiscida by concentric growth in the equatorial plane. In the same way in which the simple chambered ring of Archidiscus is connected by radial beams with the central chamber, so in Porodiscus a variable number of concentric rings is connected with that first ring. The number of these concentric rings varies between two and ten or more, but commonly amounts to between three and five. The radial beams connecting them are either piercing or interrupted; their number increases gradually from the centre towards the periphery. The chambers between them are sometimes more regular, at other times more irregular in size and form. Their upper and lower wall is formed by the two covering "sieve-plates," or the porous cover-plates, which are continued from the central disk to the margin. If these two sieve-plates continue being parallel, the disk becomes medal-shaped or a short cylinder; if the two plates become more or less concavely vaulted one against the other, the disk becomes biconvex lenticular, the middle part thicker than the marginal part. Rarely the contrary is the case, the margin thicker than the centre, and then the disk biconcave.

In my Monograph I had separated as two different subfamilies the true Trematodiscida (with circular concentric rings) from the Discospirida (with spirally convoluted rings). But the enormous mass of specimens, which I afterwards examined in the Challenger collection, has convinced me that this separation was not natural. For in one and the same genus of most nearly allied forms we find on one hand quite regular concentric circular forms (Trematodiscus), on the other hand spirally convoluted forms (Discospira), and connecting between them such forms as are in the central part concentric, in the marginal part spiral (Perispira)—or conversely, these in the centre spiral, on the margin concentric (Centrospira)—and frequently also more or less irregular forms with interrupted rings (Atactodiscus); therefore, all those genera (Prodromus, 1881, Nos. 448-452) have only the value of subgenera of Porodiscus. But a distinct genus is Perichlamydium, in which the two sieve-plates run on the margin of the lens and form a broad hyaline porous or solid girdle. More important is the distinction of the Ommatodiscida, in which the margin of the disk exhibits one larger osculum, armed with a corona of spines (Ommatodiscus), or two oscula, opposite on the poles of one axis (Stomatodiscus). Whilst in many Porodiscida all chambers of the concentric rings lie in one and the same (equatorial) plane, in many others with further growth they become stratified in floors, and the whole disk is therefore composed of two to four or more parallel disks, each with a system of concentric chambered rings or girdles, quite as in the majority of the Coccodiscida (p. 457). Often the central part of the lenticular disk becomes thickened by apposition of such floors or strata, whilst the marginal part remains simple, with one single stratum. The communication between the chambers of the different strata seems to be the same as in the similar Coccodiscida.

Also the margin of the disk exhibits in the Porodiscida the same characteristic differences as in the foregoing family. In the subfamily of Stylodictyida it bears a certain number of solid radial spines, often regularly disposed (as in the Stylocyclida). In the subfamily of Euchitonida the margin is distinguished by the possession of two to six or more (commonly three or four) chambered arms, also situated in the plane of the disk, and of the same structure (sometimes more or less irregular, spongy). These arms are very variable in size, form, and structure, exhibit the same peculiarities as in the Astracturida, and are sometimes free, at other times connected by a "patagium" or an interbrachial spongy skeleton of different structure, like a web membrane (compare above, p. 458). In some genera the arms become forked or branched on the distal end. Sometimes their distal end bears a terminal radial spine.

The Central Capsule of the Porodiscida assumes generally the form of the including shell, with or without arms, but is constantly somewhat smaller, as it remains enclosed by the sieve-plates of the disk surface. Often the capsule is filled with many coloured oil-globules, disposed regularly in the chamber rows. The nucleus of it is enclosed by the central chamber, and in many cases by this and the innermost concentric rings.

Synopsis of the Genera of the Porodiscida.

I. Section of the Porodiscida—Archidiscaria. Central chamber of the disk surrounded only by one single chambered ring.
1. Subfamily Archidiscida. Only one single chambered girdle surrounds the central chamber; margin smooth or spiny.					$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Margin smooth, without spines,			212. Archidiscus.
						Margin armed with radial spines,			213. Axodiscus.
II. Section of the Porodiscida—Astrodiscaria. Central chamber of the disk surrounded by two or more (commonly three to six) concentric chambered rings or radiated girdles.
2. Subfamily Trematodiscida. Margin of the disk quite simple, without radial appendages (spines or chambered arms), without peculiar oscula.					$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Margin simple, without an equatorial girdle,			214. Porodiscus.
						Margin with a thin porous equatorial girdle,			215. Perichlamydium.
3. Subfamily Ommatodiscida. Margin of the disk without chambered arms but distinguished by one or two large oscula, or wide openings armed with a crown of spines.					$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Disk with a single marginal osculum,			216. Ommatodiscus.
						Disk with two opposite marginal oscula,			217. Stomatodiscus.
4. Subfamily Stylodictyida. Margin of the disk without peculiar oscular openings and without chambered arms, but armed with solid radial spines.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Radial spines of the margin two, three, or four, usually quite regularly disposed.			$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Two opposite spines,			218. Xiphodictya.
						Three equidistant spines,			219. Tripodictya.
						Four crossed spines,			220. Staurodictya.
		Radial spines of the margin five or more, commonly irregularly disposed (generally ten to twelve).			$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Margin simple, without an equatorial girdle,			221. Stylodictya.
						Margin with a thin porous equatorial girdle,			222. Stylochlamydium.
5. Subfamily Euchitonida. Margin of the disk with radial chambered arms (or hollow chambered appendages), on the distal end of the arms with or without solid radial spines.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Two arms, opposite in one main axis.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Two arms simple, undivided.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without a patagium,			223. Amphibrachium.
						With a patagium,			224. Amphymenium.
				Two arms forked (or one simple, other forked).	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without a patagium,			225. Amphirrhopalum.
						With a patagium,			226. Amphicraspedum.
		Three arms (either regular, equal, or bilateral, with unequal arms).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Three arms simple, undivided.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Without a patagium.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Regular,	227. Dictyastrum.
								Bilateral,	228. Rhopalastrum.
						With a patagium.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Regular,	229. Hymeniastrum.
								Bilateral,	230. Euchitonia.
				Three arms forked.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Either regular or bilateral.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Without a patagium,	231. Chitonastrum.
								With a patagium,	232. Trigonastrum.
		Four arms (either regular, with four equal crossed arms, or bilateral, with paired arms).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Four arms simple, undivided.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Without a patagium.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Regular,	233. Stauralastrum.
								Bilateral,	234. Hagiastrum.
						With a patagium.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Regular,	235. Histiastrum.
								Bilateral,	236. Tessarastrum.
						With a terminal patagial girdle,			237. Stephanastrum
				Four arms forked.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without a patagium.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Regular,	238. Dicranastrum.
								Bilateral,	239. Myelastrum.
		Five arms (equal or unequal).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Five arms simple, undivided.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without a patagium,			240. Pentalastrum.
						With a patagium,			241. Pentinastrum.
				Five arms forked.		Without a patagium,			242. Pentophiastrum.
		Six arms (equal or unequal).	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Six arms simple, undivided.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without a patagium,			243. Hexalastrum.
						With a patagium,			244. Hexinastrum.

Subfamily 1. Archidiscida, Haeckel.

Definition.—Porodiscida with a simple spherical or lenticular latticed central chamber, surrounded by a single concentric latticed ring, which is divided by radial beams into two to six or more radial chambers.

Genus 212. Archidiscus,^[38] n. gen.

Definition.—Porodiscida with a simple central chamber, surrounded by a single concentric ring, which is divided by radial beams into two to six or more radial chambers, without radial spines on the margin.

The genus Archidiscus begins the long and polymorphous series of the Cyclodiscaria or of those Discoidea which do not possess the peculiar "phacoid shell" characteristic of the three preceding families, united as "Phacodiscaria." As already mentioned above, both these groups are probably of independent origin, derived from the Sphæroidea in different ways (compare pp. 402, 405, &c.). Among all Cyclodiscaria Archidiscus is the most simple, and probably the common ancestral form, from which the other genera may be derived.

Subgenus 1. Dioniscus, Haeckel.

Definition.—Ring with two chambers, separated by two radial beams.

1. Archidiscus dioniscus, n. sp.

Ring circular, connected with the central chamber by two radial beams, opposite in one axis, therefore two equal semicircular ring chambers. (This primitive form has an interesting reference to Saturnalis, Pl. 13, fig. 16, and differs from it only in the lattice-work covering both faces of the lenticular disk, the margin of which forms the ring.)

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.016.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

2. Archidiscus dithalamus, n. sp.

Ring roundish, connected with the central chamber by two radial beams, not opposite in one axis; both semicircular ring chambers more or less unequal, one of them larger than the other, and sometimes much more prominent. (If this prominence increase, we can regard it as the beginning of spiral convolutions, Discospira.)

Dimensions.—Diameter of the ring 0.06, of the central chamber 0.014.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

Subgenus 2. Trioniscus, Haeckel.

Definition.—Ring with three chambers, separated by three radial beams.

3. Archidiscus trioniscus, n. sp.

Ring triangular, roundish, equilateral, connected with the central chamber by three radial beams at equal distances (120°); therefore three equal ring chambers. (Resembles the central part of the disk of Tripodictya trigonaria, Pl. 42, fig. 8, and may be the ancestral form of it.)

Dimensions.—Diameter of the ring 0.04, of the central chamber 0.014.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

4. Archidiscus trithalamus, n. sp.

Ring irregular, roundish, connected with the central chamber by three radial beams at unequal distances; therefore three ring chambers of different size. (If these differences be important, they introduce a spiral convolution in the further development of the Porodiscus arising from it.)

Dimensions.—Diameter of the ring 0.06, of the central chamber 0.016.

Habitat.—South Pacific, Station 288, surface.

Subgenus 3. Tetroniscus, Haeckel.

Definition.—Ring with four chambers, separated by four radial beams.

5. Archidiscus stauroniscus, n. sp. (Pl. 48, figs. 9, 9a).

Ring regular, square, connected with the central chamber by four radial beams at equal distances, opposite in pairs in two axes perpendicular one to another; therefore four equal ring chambers (or congruent quadrants of the ring). Resembles the central part of the disk of Staurodictya medusa, &c. (Pl. 42, figs. 1-3); also of Staurodictya gracilis, Ehrenberg, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxiii. fig. 3).

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.016.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

6. Archidiscus tetroniscus, n. sp.

Ring elliptical, of rhomboidal fundamental form, connected with the central chamber by four radial beams, halving the sides of the rhombus and opposite in pairs in two axes which are not perpendicular one to another; therefore four ring chambers in pairs different, two opposite equal and larger than the two others.

Dimensions.—Diameter of the ring 0.05 to 0.07, of the central chamber 0.016.

Habitat.—Central Pacific, Station 263, depth 2650 fathoms.

7. Archidiscus tetrathalamus, n. sp.

Ring irregular, quadrangular, connected with the central chamber by four radial beams of increasing unequal length; therefore all four ring chambers of different size, gradually increasing in the following quadrants of the ring. Important as an ancestral type of such spiral and semi-spiral forms as Staurodictya cruciata (Pl. 42, figs. 4, 12, &c.) and Stylodictya clavata, Stylodictya stellata, &c., of Ehrenberg, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxiii. figs. 2, 7, 8, 9).

Dimensions.—Diameter of the ring 0.05 to 0.08, of the central chamber 0.06.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

Subgenus 4. Pentoniscus, Haeckel.

Definition.—Ring with five chambers, separated by five radial beams.

8. Archidiscus pentoniscus, n. sp.

Ring pentagonal or nearly circular, regular, connected with the central chamber by five radial beams of equal length and at equal distances (72°); therefore all five chambers of the ring of equal size and similar form. (Resembles the central part of the disk of Pentinastrum asteriscus, Pl. 44, fig. 2.)

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.015.

Habitat.—North Pacific, Station 244, surface.

Subgenus 5. Hexoniscus, Haeckel.

Definition.—Ring with six chambers, separated by six radial beams.

9. Archidiscus hexoniscus, n. sp. (Pl. 48, figs. 10, 10a).

Ring regular, hexagonal, or nearly circular, connected with the central chamber by six radial beams of equal length and at equal distances (60°); therefore all six chambers of the same size and form. (Resembles the central part of the disk of Hexinastrum geryonidum, Pl. 44, fig. 4.)

Dimensions.—Diameter of the ring 0.06, of the central chamber 0.018.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

10. Archidiscus pyloniscus, n. sp. (Pl. 48, figs. 11, 11a).

Ring triangular, connected with the central chamber by six radial beams at alternating distances; therefore three larger chambers (of looser network) alternate with three smaller chambers (of denser network); pores of the former twice to three times as large as those of the latter. This species is of peculiar importance, as an immediate transitional form to the Pylodiscida. If these three larger ring chambers lose their few lattice-beams and so became open gates, we get Triolene or Triopyle, the original forms of the Pylodiscida.

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.015.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

11. Archidiscus hexathalamus, n. sp.

Ring irregular, roundish, or hexagonal, connected with the central chamber by six radial beams of unequal increasing length; therefore all six ring chambers of gradually increasing size (beginning a spiral convolution, original form of some Discospira).

Dimensions.—Diameter of the ring 0.05 to 0.07, of the central chamber 0.014.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

Subgenus 6. Circoniscus, Haeckel.

Definition.—Ring with seven or more chambers, separated by seven or more radial beams.

12. Archidiscus octoniscus, n. sp.

Ring circular or regular octagonal, connected with the central chamber by eight equidistant radial beams; therefore eight ring chambers of equal size. (Compare the central part of the disk of Porodiscus quadrigatus, Pl. 41, fig. 3.)

Dimensions.—Diameter of the ring 0.04, of the central chamber 0.014.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

13. Archidiscus polythalamus, n. sp.

Ring circular, connected with the central chamber by nine to ten or more radial beams at nearly equal distances. Ring chambers nine to ten, more or less equal, sometimes also eleven to twelve, more different. (This species is very variable, and may perhaps be divided into a number of different "transformistic species.")

Dimensions.—Diameter of the ring 0.04 to 0.06, of the central chamber 0.015.

Habitat.—Central Pacific, Stations 265 to 274, depths 2350 to 2925 fathoms.

Genus 213. Axodiscus,^[39] n. sp.

Definition.—Porodiscida with a simple central chamber, surrounded by one single concentric ring, which is divided by radial beams into two to six or more radial chambers; margin of the disk armed with radial spines.

The genus Axodiscus differs from the preceding Archidiscus only in the shape of the margin of the small lenticular disk, which is armed with a variable number of radial spines, indicating certain axes or radii of the shell. If these marginal spines at certain equal distances from the margin branch and their distal ends become united by these branches forming a concentric second ring, the genus passes into Porodiscus. The different number and disposition of the marginal spines are probably very important, as determining the later development of two to four or more radii in the different genera of Porodiscida.

1. Axodiscus stylophorus, n. sp.

Ring circular, with two equal semicircular chambers, connected with the central chamber by two opposite radial beams, which are prolonged outside into two strong conical spines.

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.016.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Axodiscus triradiatus, n. sp.

Ring regular, triangular, equilateral, connected with the central chamber by three equidistant radial beams, which are prolonged outside into three short conical spines. (Differs from Archidiscus trioniscus in the possession of marginal spines.)

Dimensions.—Diameter of the ring 0.04, of the central chamber 0.013.

Habitat.—Central Pacific, Station 267, depth 2700 fathoms.

3. Axodiscus staurophorus, n. sp.

Ring regular, square, connected with the central chamber by four radial beams, which lie opposite in pairs in two perpendicularly crossed axes, and are prolonged outside into four delicate cylindrical spines.

Dimensions.—Diameter of the ring 0.045, of the central chamber 0.015.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

4. Axodiscus hexagonus, n. sp.

Ring regular, hexagonal, connected with the central chamber by six radial beams at equal distances, which are prolonged outside into six strong pyramidal spines.

Dimensions.—Diameter of the ring 0.06, of the central chamber 0.018.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

5. Axodiscus trigonus, n. sp.

Ring regular, triangular, equilateral, connected with the central chamber by six radial beams of alternating length and distance; therefore three smaller (perradial) chambers (with denser and darker network) alternating with three larger (interradial) chambers (with looser and finer network). On the margin three strong conical radial spines, arising in the radius of the larger chambers. (Differs from Archidiscus pyloniscus, Pl. 48, fig. 11, mainly in the strong angular spines on the three corners of the triangular shell.)

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.014.

Habitat.—South Pacific, Station 296, depth 1825 fathoms.

6. Axodiscus octogonus, n. sp.

Ring circular or nearly octagonal, connected with the central chamber by eight radial beams at nearly equal distances, which are prolonged outside into eight short conical spines. (Differs from Archidiscus octoniscus in the marginal prolongation of the eight beams.)

Dimensions.—Diameter of the ring 0.04, of the central chamber 0.013.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

7. Axodiscus spinosus, n. sp.

Ring circular, connected with the central chamber by ten to twelve radial beams at nearly equal distances, which are prolonged outside into short conical spines of variable length. (May be regarded as an aculeate variety of Archidiscus polythalamus.)

Dimensions.—Diameter of the ring 0.04 to 0.05, of the central chamber 0.014.

Habitat.—Central Pacific, Stations 265 to 274, depths 2350 to 2950 fathoms.

Subfamily 2. Trematodiscida, Haeckel, 1862, Monogr. d. Radiol., p. 491 (sensu emendato et restricto).

Definition.—Porodiscida without radial appendages of the disk (solid spines or chambered arms on the margin), and without peculiar oscula on the margin of the disk, which is composed of two to four or more concentric rings.

Genus 214. Porodiscus,^[40] Haeckel, 1881, Prodromus, p. 459.

Definition.—Porodiscida with simple circular disk, composed of several rings (without radial appendages or peculiar oscula on the margin of the disk).

The genus Porodiscus is, next to its ancestral form, Archidiscus, the simplest and most primitive form of the Porodiscida, from which all other genera of this family can be derived. The disk is quite simple, without any marginal appendages, composed of a variable number of rings, commonly of circular form, sometimes more or less polygonal, elliptical, or irregular. In my Monograph (1862, pp. 491, 513) I had separated the species, here united in Porodiscus, into two different genera: Trematodiscus with concentric rings, and Discospira with spiral rings. But the extended study of these very common forms in a great number of specimens in the Challenger collection has convinced me that the separation of those two genera cannot be maintained. In one and the same locality, where one single characteristic disk-form is very common, we find intermingled quite regular disks with only concentric, circular rings (Trematodiscus), and other disks with one single perfect spiral ring (Discospira); and between these a smaller number of specimens, in which the rings of the disk are partly concentric, partly spiral; either the rings of the central part of the disk are concentric, the outer spiral (Perispira), or the proportion is inverse (Centrospira); and sometimes the whole disposition of the concentric and spiral rings is irregular, and the rings often interrupted (Atactodiscus). Therefore it appears more natural to give to all these different forms only the value of subgenera of Porodiscus, as I have already proposed in my Prodromus (1881, p. 459). Even the numerous species of Porodiscus (mainly characterised by the equal or different breadth of the rings, and by the number, form, and size of the connecting radial beams and of the superficial pores) are for the most part very variable and hard to distinguish, as all those characters are not constant. Porodiscus is a quite "transformistic genus."

Subgenus 1. Trematodiscus, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 841.

Definition.—All rings of the disk concentric (commonly circular, rarely a little elliptical or polygonal).

1. Porodiscus orbiculatus, Haeckel.

Trematodiscus orbiculatus, Haeckel, 1862, Monogr. d. Radiol., p. 492, Taf. xxix. fig. 1. Trematodiscus orbiculatus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108.

All rings of the disk circular, concentric, of equal breadth, connected by numerous alternating radial beams. Chambers differing little in size, about as large as the central chamber. Pores regular, circular, two to two and a half on the breadth of each ring.

Dimensions.—Diameter of the disk (with nine rings) 0.18; breadth of each ring 0.01; pores 0.003.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface; also fossil in Tertiary rocks of Barbados, Sicily, and Nicobar.

2. Porodiscus concentricus, Haeckel.

Trematodiscus concentricus, Haeckel, 1862, Monogr. d. Radiol., p. 493.

Trematodiscus concentricus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108.

Flustrella concentrica, Ehrenberg, 1838, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 132; Ibid., 1875, p. 72, Taf. xxii. fig. 13.

? Flustrella concentrica, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 61, Taf. xx. fig. 42, Taf. xxi. fig. 51, Taf. xxxvi. fig. 29.

All rings of the disk circular, concentric, of equal breadth, connected by numerous piercing radial beams. Chambers different in size, increasing from the centre towards the periphery. Pores regular, circular, one and half to two on the breadth of each ring.

Dimensions.—Diameter of the disk (with eight rings) 0.16; breadth of each ring 0.01; pores 0.003.

Habitat.—Fossil in many Tertiary rocks—Barbados, Sicily, Greece, &c.

3. Porodiscus flustrella, n. sp. (Pl. 41, fig. 1).

Trematodiscus flustrella, Haeckel, 1866, MS. Canar. Ins.

All rings of the disk circular, concentric, of equal breadth, connected by numerous piercing radial beams. Chambers different in size, increasing from the centre towards the periphery. Pores very irregular, polygonal, or roundish, one to three on the breadth of each ring.

Dimensions.—Diameter of the disk (with six rings) 0.12; breadth of each ring 0.01; pores 0.002 to 0.006.

Habitat.—Cosmopolitan; Atlantic, Pacific, &c., many Stations, surface.

4. Porodiscus sorites, Haeckel.

Trematodiscus sorites, Haeckel, 1862, Monogr. d. Radiol., p. 492, Taf. xxix. fig. 2.

All rings of the disk circular, concentric, of equal breadth, connected by numerous alternating radial beams. Chambers different in size, increasing from the centre. Pores regular, circular, one to one and a half on the breadth of each ring.

Dimensions.—Diameter of the disk (with six rings) 0.12; breadth of each ring 0.01; pores 0.006.

Habitat.—Mediterranean (Messina), surface.

5. Porodiscus macroporus, Haeckel.

Trematodiscus macroporus, Haeckel, 1879, MS. Flustrella macropora, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 160.

All rings of the disk circular, concentric, of equal breadth, connected by numerous piercing radial beams. Chambers of different breadth, increasing from the centre. Pores regular, very large, nearly square, one single pore on the breadth of each ring.

Dimensions.—Diameter of the disk (with five rings) 0.11; breadth of each ring 0.01; pores 0.005.

Habitat.—Fossil in the Tertiary rocks of Barbados.

6. Porodiscus microporus, Haeckel.

Trematodiscus microporus, Stöhr, 1880, Palæontogr., vol xxvi. p. 108, Taf. iv. fig. 17.

All rings of the disk concentric, either circular or a little elliptical; the innermost rings of the same breadth as the central chamber, the third ring much broader. Radial beams between them alternating; chambers of different size. Pores very small, subregular, everywhere of the same size, four to five pores on the breadth of each ring.

Dimensions.—Diameter of the disk (with three rings) 0.15; breadth of the inner rings 0.02, of the outer 0.03; pores 0.0016.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

7. Porodiscus ellipticus, Haeckel.

Trematodiscus ellipticus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108, Taf. iv. fig. 16.

All rings of the disk concentric, either circular or a little elliptical, connected by eight piercing radial beams; central chamber elliptical, of the same breadth as the first ring, broader than the following rings, the breadth of which decreases towards the periphery. Pores irregular, in the inner rings twice as broad as in the outer (third) ring, four to five on the breadth of each ring.

Dimensions.—Diameter of the disk (with three rings) 0.18; breadth of the inner rings 0.03, of the outer 0.02; pores 0.003 to 0.006.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

8. Porodiscus heterocyclus, Haeckel.

Trematodiscus heterocyclus, Haeckel, 1862, Monogr. d. Radiol., p. 493, Taf. xxix. fig. 3.

? Flustrella cyclia, Harting, 1863, Fauna Banda-Zee, p. 11, pl. i. fig. 19.

Trematodiscus heterocyclus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108.

All rings of the disk concentric, circular, connected by numerous radial beams, which are partly piercing, partly alternating. The breadth of the rings increases gradually from the centre towards the periphery, corresponding also to the size of the pores; two to three circular pores on the breadth of each ring.

Dimensions.—Diameter of the disk (with six rings) 0.17; breadth of the second ring 0.007, of the sixth 0.02; pores 0.002 to 0.006.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in Tertiary rocks of Barbados and the Mediterranean.

9. Porodiscus quadrigatus, n. sp. (Pl. 41, fig. 3).

All rings of the disk concentric, of nearly equal breadth, connected by four interradial beams, perpendicular one to another. The first ring (surrounding the central chamber) with eight chambers, the second only with four (alternating with the four radial beams). Size of the four chambers of each ring increases much towards the periphery. Pores regular, circular, about two on the breadth of each ring.

Dimensions.—Diameter of the disk (with six rings) 0.18; breadth of each ring 0.05; pores 0.004.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Subgenus 2. Perispira, Haeckel, 1881, Prodromus, p. 459.

Definition.—The inner rings of the disk concentric (commonly circular); the outer rings spirally convoluted.

10. Porodiscus perispira, n. sp. (Pl. 41, fig. 2).

Perispira perforata, Haeckel, 1881, Prodromus.

Inner rings of the disk (two or three) concentric, outer rings (three or four) spirally convoluted, spiral line simple. All rings nearly of the same breadth, connected by alternating irregular radial beams. Pores irregular, two to three on the breadth of each ring.

Dimensions.—Diameter of the disk (with six rings) 0.17; breadth of each ring 0.016; pores 0.003 to 0.005.

Habitat.—Pacific, central area, Stations 272 to 274, surface.

11. Porodiscus radiatus, n. sp.

Perispira radiata, Haeckel, 1881, Prodromus.

Inner rings of the disk (four or five) concentric, outer rings (three or four) spirally convoluted, spiral line simple. All rings connected by piercing radial beams (eight in the inner half, sixteen in the outer half). Breadth of the rings and of the pores increasing from the centre towards the periphery, three to four pores on the breadth of each ring.

Dimensions.—Diameter of the disk (with eight rings) 0.18; breadth of the second ring 0.006, of the eighth ring 0.02; pores 0.002 to 0.006.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Subgenus 3. Centrospira, Haeckel, 1881, Prodromus, p. 459.

Definition.—The inner rings of the disk spirally convoluted, the outer rings concentric (commonly circular).

12. Porodiscus centrospira, n. sp. (Pl. 41, fig. 6).

Centrospira perispongidium, Haeckel, 1881, Prodromus.

Inner rings of the disk (two or three) spirally convoluted (with simple or double spiral line), outer rings (three or four) concentric, subcircular. All rings nearly of the same breadth, connected by alternating radial beams. Pores subregular, two to three on the breadth of each ring. Lattice-work in the periphery of the disk a little spongy (as in Pl. 41, fig. 11).

Dimensions.—Diameter of the disk (with five rings) 0.15; breadth of each ring 0.015; pores 0.003.

Habitat.—Pacific, central area, Station 267, depth 2700 fathoms.

Subgenus 4. Discospira, Haeckel, 1862, Monogr. d. Radiol., p. 513.

Definition.—All rings of the disk spirally convoluted, forming parts of a simple or double spiral turning.

13. Porodiscus helicoides, Haeckel.

Discospira helicoides, Haeckel, 1862, Monogr. d. Radiol., p. 514, Taf. xxix. fig. 7. Trematodiscus helicoides, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 841.

All rings of the disk spirally convoluted around the central chamber; spiral line regular, simple. All rings nearly of the same breadth, connected by numerous alternating radial beams. Chambers little different in size, little longer than broad. Pores of equal size, regular, two on the breadth of each ring.

Dimensions.—Diameter of the disk (with ten rings) 0.2; breadth of each ring 0.01; pores 0.0025.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific; also fossil in the Tertiary rocks of the Mediterranean, Sicily, Oran, &c.

14. Porodiscus spiralis, Haeckel.

Flustrella spiralis, Ehrenberg, 1840, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 210; Mikrogeol., 1854, Taf. xix. fig. 62. Discospira spiralis, Haeckel, 1862, Monogr. d. Radiol., p. 513.

All rings of the disk spirally convoluted around the central chamber; spiral line regular, simple. All rings nearly of the same breadth, connected by numerous (twelve to sixteen) piercing radial beams. Chambers increasing in size from the centre towards the periphery. Pores irregular, of different size, one and a half to two on the breadth of each ring.

Dimensions.—Diameter of the disk (with eight rings) 0.16; breadth of each ring 0.01; pores 0.004.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific; also fossil in the Tertiary rocks of Barbados, Sicily, Greece, &c.

15. Porodiscus operculina, Haeckel.

Discospira operculina, Haeckel, 1862, Monogr. d. Radiol., p. 514, Taf. xxix. fig. 8.

All rings of the disk spirally convoluted around the central chamber, spiral line regular, simple. Breadth of the rings and length of the chambers increasing in size from the centre towards the periphery. Most part of chambers twice as long as broad. Pores irregular, of very different sizes, two to three on the breadth of each ring.

Dimensions.—Diameter of the disk (with six rings) 0.16; breadth of the rings 0.012 to 0.016; pores 0.002 to 0.006.

Habitat.—Mediterranean (Messina), surface.

16. Porodiscus bilix, Haeckel.

Discospira bilix, Stöhr, 1880, Palæontogr., vol. xxvi. p. 113, Taf. vi. fig. 3.

All rings of the disk spirally convoluted around the large elliptical central chamber. Spiral convolutions of the inner rings simple, of the outer rings double; the latter twice as broad as the former. Pores regular, circular, in the inner rings one pore on the breadth, in the outer rings two to three pores. Radial beams piercing, numerous, on the margin prominent.

Dimensions.—Diameter of the disk (with six rings) 0.14; breadth of the inner rings 0.007, of the outer 0.013; pores 0.0017.

Habitat.—Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.

17. Porodiscus bispiralis, Haeckel.

Stylodictya bispiralis, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 160. Taf. xxiv. fig. 1.

All rings of the disk spirally convoluted, in a perfect double spiral, with increasing breadth of the rings; the fourth ring twice as broad as the first. Pores regular, circular; in the inner rings one pore on the breadth, in the outer rings two to three pores. Radial beams piercing, numerous, prominent on the margin.

Dimensions.—Diameter of the disk (with four rings) 0.1; breadth of the inner rings 0.006, of the outer 0.012; pores 0.0015.

Habitat.—Fossil in the rocks of Barbados; living in the depths of the Central Pacific, Station 268, depth 2900 fathoms.

18. Porodiscus duplex, Haeckel.

Discospira duplex, Stöhr, 1880, Palæontogr., vol. xxvi. p. 114, Taf. vi. fig. 4.

All rings of the disk spirally convoluted, in a perfect double spiral, with increasing breadth of the broad rings. Pores regular, circular; in the inner rings two to three, in the outer four to five on the breadth. Radial beams interrupted. Margin of the rings thorny.

Dimensions.—Diameter of the disk (with three rings) 0.15; breadth of the rings 0.02 to 0.04; pores 0.007.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

19. Porodiscus semispiralis, n. sp. (Pl. 41, fig. 4).

All rings of the disk spirally convoluted, divided by four radial, perpendicularly crossed and zigzag shaped beams into four quadrants; the quarter rings of each quadrant halving the rings of each adjacent quarter. Half spiral line often irregular or partly interrupted. Breadth of all rings nearly equal. Pores irregular, roundish, two on the breadth of each ring. Margin of the disk dentated.

Dimensions.—Diameter of the disk (with nine rings) 0.22; breadth of each ring 0.012; pores 0.002 to 0.006.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

Subgenus 5. Atactodiscus, Haeckel, 1881, Prodromus, p. 459.

Definition.—Rings of the disk more or less irregular, partly concentric, partly spirally convoluted, often interrupted.

20. Porodiscus deformis, Haeckel.

Discospira deformis, Stöhr, 1880, Palæontogr., vol. xxvi. p. 114, Taf. vi. fig. 6.

Rings of the disk irregular, partly concentric, partly spiral, often interrupted, increasing in breadth from the centre. Radial beams not piercing; pores regular, circular, two to six on the breadth of the different rings. (Very variable and irregular, sometimes more spiral, at other times more concentric, but always with equal pores.)

Dimensions.—Diameter of the disk (with four rings) 0.18; breadth of the first ring 0.014, of the second 0.03, of the fourth 0.06; pores 0.005.

Habitat.—Fossil in the Tertiary rocks of Barbados and Sicily; living in the Central Pacific, Stations 266 to 268, depths 2700 to 2900 fathoms.

21. Porodiscus irregularis, n. sp. (Pl. 41, fig. 7).

Atactodiscus irregularis, Haeckel, 1881, Prodromus, p. 459. Perispongidium irregulare, Haeckel, 1878, MS. et Atlas (pl. xli. fig. 7).

Rings of the disk irregular, partly concentric, partly spiral, often interrupted, with nearly equal breadth. Radial beams not piercing; pores irregular, roundish, two to four on the breadth of each ring; network in the periphery of the disk spongy. (Very variable and irregular, sometimes more spiral, at other times more concentric; disk in the peripheral part often more or less spongy. Differs from the preceding by the equal breadth of the rings and the different size of the pores.)

Dimensions.—Diameter of the disk (with six rings) 0.15; breadth of each ring 0.011; pores 0.002 to 0.004.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in Barbados.

Genus 215. Perichlamydium,^[41] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Porodiscida with a simple circular disk (without radial spines and chambered arms), surrounded on the margin by a thin porous (but not chambered) equatorial girdle.

The genus Perichlamydium differs from Porodiscus only in the development of a thin, porous, equatorial girdle, which surrounds the circular margin of the chambered disk. This girdle lies in the equatorial plane of the lenticular disk, and represents a very delicate siliceous plate, perforated by numerous small pores. Sometimes the proximal part of the girdle is ribbed by thin radial beams, the distal prolongations of the radial rods of the central disk. If these ribs reach the margin of the girdle and are prominent over it, Perichlamydium passes over into Stylochlamydium.

1. Perichlamydium praetextum, Ehrenberg.

Perichlamydium praetextum, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 43; Mikrogeol., 1854, Taf. xxii. fig. 21 (non 20). Perichlamydium praetextum, Haeckel, 1862, Monogr. d. Radiol., p. 495.

All rings of the disk (three to four) concentric, circular, of equal breadth, with interrupted (not piercing) radial beams. Equatorial girdle without radial beams, nearly as broad as the disk; its circular pores of the same size as those of the disk; about two pores on the breadth of each ring.

Dimensions.—Diameter of the disk (without the girdle, with four rings) 0.11; breadth of each ring 0.012; breadth of the girdle 0.06 to 0.1; pores 0.004.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, surface; also fossil in the Tertiary rocks of Barbados and Sicily.

2. Perichlamydium saturnus, n. sp. (Pl. 41, fig. 5).

All rings of the disk (three to four) concentric, circular (sometimes partly concentric, circular, partly spiral, or irregular), with interrupted (not piercing) radial beams. Equatorial girdle without radial beams, about half as broad as the disk; its circular pores very small, scarcely half as large as those of the disk; about three pores on the breadth of each ring. (Very variable in the ring-form, differs from the preceding in the small pores of the girdle.)

Dimensions.—Diameter of the disk (without the girdle, with three rings) 0.11; breadth of each ring 0.02, pores 0.004, breadth of the girdle 0.05, pores 0.002.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

3. Perichlamydium accrescens, Haeckel.

Discospira accrescens, Stöhr, 1880, Palæontogr., vol. xxvi. p. 114, Taf. vi. fig. 5.

All rings of the disk (six to seven) not concentric, convoluted in a simple spiral, of nearly equal breadth, with interrupted (not piercing) radial beams. Equatorial girdle in the proximal part with numerous radial beams, which do not reach its margin; its pores half as large as those of the disk, where one to two pores arise on the breadth of each ring. (The girdle becomes twice to three times as broad as in the figure of Stöhr.)

Dimensions.—Diameter of the disk (with seven rings, without the girdle) 0.13; breadth of each ring 0.007 to 0.01; pores 0.0036; breadth of the girdle 0.05, pores of it 0.0017.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Haeckel); living in the Central Pacific, Station 266, depth 2750 fathoms.

4. Perichlamydium spirale, Ehrenberg.

Perichlamydium spirale, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 80, Taf. xxii. fig. 12.

All rings of the disk (three to four) not concentric, convoluted in a simple spiral, of increasing breadth from the centre; connected by numerous piercing radial beams. Equatorial girdle about half as broad as the disk, without radial beams; its pores of the same size as those of the disk, regular, circular; three pores on the breadth of the first ring, six pores of the fourth ring.

Dimensions.—Diameter of the disk (with four rings, without the girdle) 0.12; breadth of the first ring 0.01, of the fourth 0.02; breadth of the girdle 0.05; pores 0.003.

Habitat.—Fossil in the rocks of Barbados.

Subfamily 3. Ommatodiscida, Stöhr, 1880, Palæontographica, vol. xxvi. p. 115.

Definition.—Porodiscida without radial appendages of the concentrically annulated disk, but distinguished by one single or two opposite large marginal oscula, or wide openings on the margin of the disk, armed with a coronet of spines.

Genus 216. Ommatodiscus,^[42] Stöhr, 1880, Palæontographica, vol. xxvi. p. 115.

Definition.—Porodiscida without chambered arms and radial spines on the margin of the circular or elliptical disk, but with one large marginal osculum or opening surrounded by a coronet of spines.

The genus Ommatodiscus, together with the following Stomatodiscus, form the peculiar small subfamily of Ommatodiscida, founded by Stöhr in 1880 (loc. cit.). These remarkable Porodiscida, very nearly allied to Porodiscus, are distinguished by one or two large openings on the margin of the disk, and these "marginal oscula" are constantly armed with a coronet of spines (comparable to the osculum coronatum of Sycon in the Calcispongiæ). Probably in the living Ommatodiscida the osculum is the door from which a "sarcode-flagellum" issues (comp. above, p. 407). Perhaps this osculum is comparable to the peculiar coronet of spines which is developed on one pole of the shell axis in some Ellipsida (Lithomespilus, Lithapium). The internal structure of the disk is commonly more or less obscure, as the lenticular disk is much thickened, sometimes nearly ellipsoidal. It is possible that the Ommatodiscida are more nearly related to the Lithelida than to the Porodiscida; but there is no indication of an internal trizonal medullary shell. Also the apparent resemblance to the Cyrtida is of no morphological value; both groups are of quite independent phylogenetic origin.

Subgenus 1. Ommatodiscinus, Haeckel.

Definition.—Disk circular.

1. Ommatodiscus decipiens, Stöhr.

Ommatodiscus decipiens, Stöhr, 1880, Palæontogr., vol. xxvi. p. 115, Taf. vi. figs. 8, 8a.

Disk circular, with two chambered rings around the spherical central chamber, of equal breadth. Chambers twice as high as broad. Pores very small, one-third as broad as the bars between them, two on the breadth of each ring. Osculum of the same breadth as the central chamber, surrounded by numerous very short teeth.

Dimensions.—Diameter of the disk 0.12; breadth of the central chamber and of each ring 0.03; pores 0.0015.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

2. Ommatodiscus stöhrii, n. sp.

Disk circular with three chambered rings around the spherical central chamber, of equal breadth. Chambers broader than high. Pores of the same breadth as the bars between them, four on the breadth of each ring. Osculum of the same breadth as the central chamber, surrounded by a corona of ten to twenty thin, bristle-shaped teeth, as long as its diameter.

Dimensions.—Diameter of the disk 0.2; breadth of the central chamber and of each ring 0.03; pores 0.004.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

3. Ommatodiscus circularis, n. sp.

Disk circular, with four circular chambered rings around the spherical central chamber, of increasing breadth; the fourth ring twice as broad as the second. Chambers about as broad as high. Pores large, twice as broad as the bars, one to two on the breadth of each ring. Osculum twice as broad as the central chamber, surrounded by a coronal of strong conical teeth, twice as long as its diameter.

Dimensions.—Diameter of the disk 0.18; breadth of the central chamber and inner rings 0.015, of the outer rings 0.03; pores 0.01.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

Subgenus 2. Ommatodisculus, Haeckel.

Definition.—Disk elliptical.

4. Ommatodiscus haeckelii, Stöhr.

Ommatodiscus haeckelii, Stöhr, 1880, Palæontogr., vol. xxvi. p. 115, Taf. vi. figs. 7, 7a.

Disk elliptical (6 : 7), with four chambered rings around the elliptical central chamber, of equal breadth. Chambers about as high as broad. Pores small, half as broad as the bars, two on the breadth of each ring. Osculum three times as broad as the central chamber, surrounded by a crown of strong conical teeth.

Dimensions.—Length of the disk 0.18, breadth 0.16; breadth of each ring and of the central chamber 0.02; pores 0.003.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Haeckel).

5. Ommatodiscus lævigatus, Stöhr.

Ommatodiscus lævigatus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 116, Taf. vi. figs. 9, 9a.

Disk elliptical (3 : 4), with three chambered rings around the circular central chamber, the third ring half as broad as the second. Chambers twice as high as broad. Pores very small, one-third as broad as the bars. Osculum twice as broad as the central chamber, armed with a crown of short conical teeth.

Dimensions.—Length of the disk 0.15, breadth 0.11; breadth of inner rings 0.02, of the outer 0.01; pores 0.0017.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

6. Ommatodiscus fragilis, Stöhr.

Ommatodiscus fragilis, Stöhr, 1880, Palæontogr., vol. xxvi. p. 116, Taf. vi. figs. 10, 10a.

Disk elliptical (4 : 5), with five chambered rings around the elliptical central chamber, the fifth ring twice as broad as each of the others. Chambers about as high as broad. Pores very small, one-fifth as broad as the bars. Osculum three times as broad as the central chamber, surrounded by a coronet of short teeth.

Dimensions.—Length of the disk 0.17, breadth 0.13; breadth of the inner rings 0.01, of the outer 0.02; pores 0.001.

Habitat.—Fossil in Tertiary rocks of Sicily and Barbados; living in depths of the Tropical Atlantic and Pacific, Station 353, depth 2965 fathoms, Station 265, depth 2900 fathoms, &c.

Genus 217. Stomatodiscus,^[43] n. gen.

Definition.—Porodiscida without chambered arms and radial spines on the margin of the circular or elliptical disk, but with two large, opposite, marginal oscula, or openings surrounded by a coronet of spines.

The genus Stomatodiscus has the same characteristic structure as the foregoing Ommatodiscus, and differs from it only in the duplication of the large marginal openings. Whilst in the latter there is only one such marginal osculum, here we find on the margin of the disk two oscula, opposite on the poles of one equatorial axis.

1. Stomatodiscus amphistomus, n. sp.

Disk circular, with three concentric rings of equal breadth around the central chamber. Pores irregular, roundish, about two on the breadth of each ring. Surface of the lenticular shell spiny. On two opposite points of the margin a large osculum, three to four times as broad as the central chamber, armed with a coronet of strong pyramidal spines of different length, the longest equal to the radius of the disk.

Dimensions.—Diameter of the disk (with three rings) 0.12; breadth of each ring 0.016; pores 0.004.

Habitat.—South Pacific, Station 302, depth 1450 fathoms.

2. Stomatodiscus osculatus, n. sp. (Pl. 48, fig. 8).

Disk elliptical, nearly twice as long as broad, with three concentric rings around the elliptical central chamber, one piercing radial beam in the main axis, the other beams interrupted. Surface of the shell with small scattered thorns. Pores very irregular, roundish, partly aggregated in groups of four to eight smaller porules. On both poles of the main axis a large elliptical marginal osculum, about as large as the central chamber, armed with a coronet of short conical spines.

Dimensions.—Length of the disk (with three rings) 0.18, breadth 0.1; pores 0.001 to 0.006.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

Subfamily 4. Stylodictyida, Haeckel, 1881, Prodromus, p. 459.

Definition.—Porodiscida with solid radial spines on the margin of the concentrically annulated disk, situated in the equatorial plane of the disk (without chambered arms and marginal oscula).

Genus 218. Xiphodictya,^[44] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with two opposite, solid, radial spines on the margin of the circular or elliptical disk.

The genus Xiphodictya opens the series of the Stylodictyida or of those Porodiscida in which the margin of the chambered disk is armed with solid radial spines, all situated in the equatorial plane of the disk. Xiphodictya exhibits the minimum number of spines, two being opposite on the poles of one equatorial axis of the disk. It repeats, therefore, in this family the same amphistylic formation as Sethostylus in the Phacodiscida and Stylocyclia in the Coccodiscida.

Subgenus 1. Xiphodictyon, Haeckel.

Definition.—All rings of the disk concentric, circular.

1. Xiphodictya amphibelonia, n. sp. (Pl. 42, fig. 10).

All rings of the disk concentric, circular, of equal breadth. Pores irregular, roundish, one and a half to two on the breadth of each ring. Margin of the disk thorny, of the same thickness as the central part of the medal-shaped or cylindrical disk. Two opposite radial spines very long and thin, cylindrical, twice to three times as long as the diameter of the disk, only half as thick as the breadth of one ring.

Dimensions.—Diameter of the disk (with five rings) 0.17; breadth of each ring 0.014; pores 0.003 to 0.012.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

2. Xiphodictya amphirrhopalia, n. sp. (Pl. 42, fig. 11).

All rings of the disk concentric, circular, with increasing breadth from the centre; the fifth ring twice as broad as the second. Central chamber very large. Margin of the lenticular disk thorny, much thinner than the central part. Pores irregular, roundish, two to three on the breadth of each ring. Two opposite radial spines club-shaped, about as long as the diameter of the disk, in the outer spindle-shaped part three to four times as broad as at the base.

Dimensions.—Diameter of the disk (with six rings) 0.17; breadth of the second ring 0.008, of the fifth ring 0.016.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms; also fossil in the Tertiary rocks of Sicily (Caltanisetta).

Subgenus 2. Xiphospira, Haeckel.

Definition.—All rings of the disk or a part of them not concentric, spirally convoluted; sometimes irregular or interrupted.

3. Xiphodictya staurospira, n. sp. (Pl. 42, fig. 12).

All rings of the disk not concentric, half spiral. Four radial beams, crossed perpendicularly and zigzag-shaped, divide each ring into four quadrants; the quarter-ring of each quadrant halves the two adjacent rings. All rings of equal breadth. Pores irregular, roundish, two on the breadth of each ring. Two opposite radial spines pyramidal, somewhat shorter than the diameter of the disk.

Dimensions.—Diameter of the disk (with six rings) 0.16; breadth of each ring: 0.014; pores 0.003 to 0.007.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

4. Xiphodictya heliospira, n. sp.

All rings of the disk not concentric, convoluted in a simple, regular, spiral line; all nearly of equal breadth. Pores subregular, circular, two on the breadth of each ring. Two opposite radial spines conical, about as long as the radius of the disk. Margin of the disk thorny. (Differs from Stylodictya heliospira, Pl. 41, fig. 8, mainly by the two strong, opposite, radial spines.)

Dimensions.—Diameter of the disk (with six rings) 0.14; breadth of each ring 0.01 to 0.012; pores 0.002 to 0.006.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

Genus 219. Tripodictya,^[45] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with three solid, equidistant, radial spines on the margin of the circular or triangular disk.

The genus Tripodictya exhibits three radial spines on the margin of the disk, divergent at equal angles; rarely in some specimens the angles differ more or less. Perhaps this genus bears a near relation to the Dictyastrida (or to the Euchitonida with three chambered arms—Dictyastrum, Euchitonia, &c.).

1. Tripodictya trigonaria, n. sp. (Pl. 42, fig. 8).

All rings of the disk concentric, triangular, with three equal convex sides, all of the same breadth; first and second rings with three simple chambers, third and fourth rings with six chambers, fifth ring with twelve chambers. Central chamber also equilateral triangular, from its three corners arise three piercing perradial beams; from the second ring arise three interradial beams, alternate with the latter; from the fourth ring between these and the former arise six adradial beams. Pores subregular, two on the breadth of each ring. Three marginal spines pyramidal, as long as the radius of the disk and as broad as one ring.

Dimensions.—Diameter of the disk (with five rings) 0.11; breadth of each ring 0.011; pores 0.004.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

2. Tripodictya triacantha, n. sp. (Pl. 42, fig. 7).

All rings of the disk concentric, circular, of the some breadth, connected by very numerous irregular radial beams, the number of which increases towards the periphery. Pores irregular, roundish, two on the breadth of each ring. Three marginal spines spindle-shaped, as long as the radius of the disk, and in the middle part as broad as one ring.

Dimensions.—Diameter of the disk (with eight rings) 0.2; breadth of each ring 0.012; pores 0.004.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

3. Tripodictya tribelonia, n. sp. (Pl. 42, fig. 9).

All rings of the disk, or a part of them, not concentric, spirally convoluted, of equal breadth, connected by numerous irregular, interrupted radial beams, the number of which increases from the centre. (In one marginal view of the disk, Pl. 42, fig. 9, the disk seemed to be composed of seven parallel chambered plates in the central part, and five similar plates in the peripheral part.) Pores irregular, roundish, three on the breadth of each ring. Three marginal spines long and thin, cylindrical (as in Staurodictya cruciata, Pl. 42, fig, 4), longer than the diameter of the disk, and half as thick as one ring.

Dimensions.—Diameter of the disk (with nine rings) 0.18; breadth of each ring 0.01; pores 0.002 to 0.004.

Habitat.—Pacific, central area, Station 263, depth 2650 fathoms.

Genus 220. Staurodictya,^[46] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with four solid radial spines (commonly crossed at right angles) on the margin of the circular or quadrangular disk.

The genus Staurodictya is characterised by four marginal spines, lying opposite in pairs in two crossed equatorial diameters of the disk, perpendicular one to another. Sometimes the regular rectangular position of the spines becomes more or less irregular. Commonly the marginal spines are the extreme prolongations of four internal crossed radial beams, which are either rectilinear or zigzag-shaped. In the latter case the concentric disposition of the circular rings becomes more or less spiral. Perhaps Staurodictya has a near relation to the Stauralastrida (or to the Euchitonida with four crossed chambered arms—Stauralastrum, Histiastrum, &c.).

Subgenus 1. Staurodictyon, Haeckel.

Definition.—All rings of the disk concentric (commonly circular, sometimes with four incisions, produced by two crossed constrictions, or nearly square).

1. Staurodictya medusa, n. sp. (Pl. 42, fig. 3).

All rings of the disk concentric, of nearly equal breadth, divided into four quadrants by two perradial constrictions (perpendicular one to another). Pores irregular, roundish, two to three on the breadth of each ring. Four marginal spines strong, pyramidal, nearly as long as the radius of the disk. Margin between them denticulated.

Dimensions.—Diameter of the disk (with four rings) 0.13; breadth of each ring 0.015; pores 0.002 to 0.01.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

2. Staurodictya ciliata, n. sp. (Pl. 42, fig. 2).

All rings of the disk concentric, of nearly equal breadth, circular or roundish, without perradial constrictions. Pores subregular, circular, three to four on the breadth of each ring. Four marginal spines short, pyramidal, about as long as the breadth of one ring. Margin between them ciliated, with thin radial bristles.

Dimensions.—Diameter of the disk (with four rings) 0.13; breadth of each ring 0.015; pores 0.0025.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

3. Staurodictya elegans, n. sp. (Pl. 42, fig. 1).

All rings of the disk concentric, circular, or roundish, of increasing breadth towards the margin; the fifth ring twice as broad as the first. Pores irregular, roundish, two to three on the breadth of each ring. Four marginal spines very large, conical, with a thin pedicle at the base, cancellated by ten to twelve deep furrows, about as long as the radius of the disk and three times as long as broad at the base (above the pedicle). Margin between them ciliated, with numerous short radial spines.

Dimensions.—Diameter of the disk (with six rings) 0.14; breadth of the inner rings 0.006, of the outer 0.012; pores 0.002 to 0.008.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

4. Staurodictya quadrispina, Haeckel.

Stylodictya quadrispina, Haeckel, 1862, Monogr. d. Radiol., p. 496, Taf. xxix. fig. 4.

All rings of the disk concentric, circular, of increasing breadth towards the margin; the fourth ring twice as broad as the second. Pores irregular, roundish, two to three on the breadth of each ring. Four marginal spines short and thin, conical, about as long as the breadth of one ring. Margin between them smooth.

Dimensions.—Diameter of the disk (with six rings) 0.12; breadth of the inner rings 0.006, of the outer rings 0.012; pores 0.001 to 0.006.

Habitat.—Mediterranean, Atlantic (Canary Islands), surface.

Subgenus 2. Staurospira, Haeckel.

Definition.—All rings of the disk or a part of them not concentric, spirally convoluted; spiral line simple or double, sometimes half or irregular, interrupted.

5. Staurodictya cruciata, n. sp. (Pl. 42, figs. 4, 5).

All rings of the disk nearly of the same breadth, not concentric, half-spiral, interrupted by four zigzag-shaped radial beams crossed in two diameters perpendicular one to another. The quarter ring of each quadrant halving both neighbouring quarters. Pores irregular, roundish, two on the breadth of each ring. Pores of the outermost (eighth) ring much smaller than the others. Four marginal spines cylindrical or nearly spindle-shaped, thick, about as long as the radius of the disk. Margin between them smooth.

Dimensions.—Diameter of the disk (with eight rings) 0.2; breadth of each ring 0.011; pores 0.004.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

6. Staurodictya splendens, Haeckel.

Stylodictya splendens, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiii. fig. 9.

All rings of the disk nearly of the same breadth, not concentric, half-spiral, interrupted by four zigzag-shaped perradial beams, crossed in two diameters. The quarter ring of each quadrant halving both neighbouring quarters. Pores regular, circular, only one single on the breadth of each ring. Four marginal spines conical or spear-shaped, about half as long as the radius of the disk. Margin between them ciliated, with short bristle-shaped radial spines.

Dimensions.—Diameter of the disk (with eight rings) 0.2; breadth of each ring 0.012; pores 0.004.

Habitat.—Fossil in the rocks of Barbados.

7. Staurodictya grandis, n. sp.

All rings of the disk (twelve to sixteen) of the same breadth, not concentric, irregular, partly spiral, interrupted by irregular turnings, and by ramified radial beams, which divide each ring into numerous square chambers. Pores subregular, circular, only one single on the breadth of each ring (and on each chamber). Four marginal spines short and stout, conical, twice as long as broad at the base, four to five times as long as the breadth of one ring. Margin between them dentated.

Dimensions.—Diameter of the disk (with sixteen rings) 0.3; breadth of each ring 0.01; pores 0.005.

Habitat.—Pacific, central area, Stations 265 to 268, depth 2900 fathoms; also fossil in the Tertiary rocks of Barbados.

8. Staurodictya ocellata, Haeckel.

Stylodictya ocellata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiii. fig. 7.

All rings of the disk irregular, not concentric, half-spiral, interrupted by four zigzag-shaped, crossed, radial beams; the quarter ring of each quadrant halving both neighbouring quarters. Breadth of the rings increasing towards the periphery; the fourth ring twice as broad as the second. Pores irregular, with increasing size from the centre, three on the breadth of each ring. Four marginal spines thick and long, cylindrical; margin between them smooth.

Dimensions.—Diameter of the disk (with four rings) 0.1; breadth of the inner rings 0.01, of the outer 0.02; pores 0.002 to 0.006.

Habitat.—Fossil in the rocks of Barbados.

Genus 221. Stylodictya,^[47] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Porodiscida with numerous (five or more, commonly eight to twelve) solid radial spines, regularly or irregularly disposed on the margin of the circular or polygonal disk; margin simple, without a porous equatorial girdle.

The genus Stylodictya comprises the majority of this subfamily, in which the number of the marginal spines exceeds four. Commonly we find eight to twelve spines, more or less regularly disposed (four perradial and four interradial, or four perradial and eight adradial); but often also the number and disposition become irregular (sometimes very large). In my Monograph (1862 pp. 495, 515) I had separated the concentric disks with closed circular rings (as true Stylodictya, s. str.) from the spiral disks with convoluted rings (Stylospira). But I retain these two groups here only as two subgenera, as intermediate forms between them are very common, and often a part of the disk concentric, a part spiral (compare above, p. 492).

Subgenus 1. Stylodictyon, Haeckel, 1862, Monogr. d. Radiol., p. 495.

Definition.—All rings of the disk concentric, commonly circular (rarely a little elliptical or polygonal).

1. Stylodictya gracilis, Ehrenberg.

Stylodictya gracilis, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 28.

Stylodictya gracilis, Ehrenberg, 1873, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 257; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxiii. fig. 3.

Stylodictya gracilis, Haeckel, 1862, Monogr. d. Radiol., p. 499.

All rings of the disk concentric, circular, of equal breadth (the first ring sometimes, but not constantly, four-lobed). Pores regular, circular, small, three on the breadth of each ring. Four perradial beams (crossed in two perpendicular diameters) beginning from the circular central chamber, four interradial beams from the first or second ring (sometimes others between them). Beams prolonged into eight to twelve (or more) marginal spines, bristle-shaped, as long as the radius of the shell.

Dimensions.—Diameter of the disk (with four rings) 0.12; breadth of each ring 0.013; pores 0.0025.

Habitat.—Fossil in Tertiary rocks of Barbados and Nicobar; living in the depths of the Pacific and Atlantic.

2. Stylodictya multispina, Haeckel.

Stylodictya multispina, Haeckel, 1862, Monogr. d. Radiol., p. 496, Taf. xxix. fig. 5. Stylodictya forbesii, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 160, Taf. xxiii. fig. 6.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, two and a half to three on the breadth of each ring. Eight to twelve radial beams beginning from the central chamber, others from the inner rings. Commonly from the third or fourth ring arise twenty-four to thirty (sometimes forty or more) piercing beams, which are prolonged at the margin into bristle-shaped radial spines, as long as the breadth of two to four rings.

Dimensions.—Diameter of the disk (with seven rings) 0.2; breadth of each ring 0.013; pores 0.004.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface and various depths.

3. Stylodictya hastata, Ehrenberg.

Stylodictya hastata, Ehrenberg, 1873, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 257; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxiii. fig. 5. Stylodictya gracilis, Bury, 1862, Polycystins of Barbados, pl. ii. fig. 1.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, very small, two on the breadth of each ring. Eight to twelve marginal spines very large, spear-shaped, sulcated, pyramidal, nearly as long as the diameter of the disk, with a thin pedicle at the base, above this as thick as the breadth of one ring.

Dimensions.—Diameter of the disk (with five rings) 0.13; breadth of each ring 0.012; pores 0.003.

Habitat.—Fossil in the rocks of Barbados.

4. Stylodictya stellata, Bailey.

Stylodictya stellata, Bailey, 1856, Amer. Journ., vol. xxii. p. 6, pl. i. fig. 20. Stylodictya stellata, Haeckel, 1862, Monogr. d. Radiol., p. 499.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, very small, two on the breadth of each ring. Marginal spines fourteen (probably variable in number, twelve to sixteen), very thick and short, conical; their length seems to be equal to their basal breadth and to the breadth of one ring. Related to Stylochlamydium?

Dimensions.—Diameter of the disk (with five rings) 0.11; breadth of each ring 0.01; pores 0.003.

Habitat.—North Pacific, depths of the Kamtschatka Sea, Bailey; Station 241, depth 2300 fathoms.

5. Stylodictya arachnia, Haeckel.

Stylodictya arachnia, Haeckel, 1862, Monogr. d. Radiol., p. 497. Stylocyclia arachnia, J. Müller, 1856, p. 492; Abhandl. d. k. Akad. d. Wiss. Berlin, 1858, p. 41, Taf. i. figs. 8, 9.

All rings of the disk concentric, circular, or polygonal; their breadth increases from the centre towards the periphery, so that the fourth or fifth ring is twice as broad as the second. Pores subregular, circular, two on the breadth of each ring. Radial beams partly piercing. Marginal spines eight to sixteen (commonly twelve), bristle-shaped, very thin, once to three times as long as the diameter of the disk. (On the numerous varieties of this common species compare my Monograph, 1862, p. 498.)

Dimensions.—Diameter of the disk (with ten rings) 0.22; breadth of the inner rings 0.004 to 0.008, of the outer 0.012 to 0.015; pores 0.003 to 0.005.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

6. Stylodictya solmaris, n. sp.

All rings of the disk concentric, polygonal, with eight to sixteen rounded corners; their breadth increases from the centre; eighth ring twice as broad as the second. Pores subregular circular, large, only one pore on the breadth of each ring. Twenty to thirty marginal spines, bristle-shaped, undulating, about as long as (or longer than) the diameter of the disk.

Dimensions.—Diameter of the disk (with eight rings) 0.2; breadth of the inner rings 0.005, of the outer 0.012; pores 0.004 to 0.008.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

7. Stylodictya octogonia, n. sp.

All rings of the disk concentric, increasing in breadth from the centre. The outer rings (five to eight) regular, octogonal, twice as broad as the circular inner rings. Pores subregular, circular, two to three on the breadth of each ring. Eight piercing perradial spines (alternating with the eight corners of the octogonal rings) bristle-shaped, longer than the diameter of the disk.

Dimensions.—Diameter of the disk (with eight rings) 0.24; breadth of the inner rings 0.006, of the outer 0.014; pores 0.005 to 0.01.

Habitat.—North Atlantic, Station 353, depth 2965 fathoms.

Subgenus 2. Stylodictula, Haeckel.

Definition.—Rings of the disk partly concentric, completely annular; partly spiral or interrupted, often irregular.

8. Stylodictya perispira, n. sp.

Inner rings of the disk (two to four) concentric, circular, or roundish, outer rings forming a simple spiral, breadth a little increasing from the centre. Pores subregular, circular, about two on the breadth of each ring. Marginal spines bristle-shaped, ten to fifteen, about as long as the diameter of the disk.

Dimensions.—Diameter of the disk (with eight rings) 0.2; breadth of each ring 0.013; pores 0.004.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

9. Stylodictya centrospira, n. sp. (Pl. 41, fig. 9).

Inner rings of the disk (three or four) convoluted in a simple or double spiral, often interrupted or irregular; outer rings (two to three) concentric, circular, or roundish. Breadth of the rings variable, irregular. Pores irregular, of very different sizes, in the outer concentric part twice to four times as large as in the inner spiral part. Radial beams partly interrupted, partly piercing. Marginal spines fifty to eighty, very variable in size and number, commonly fifteen to twenty strong conical spines, twice to three times as long as the ring-breadth, and numerous (thirty to sixty) smaller spines. Very variable.

Dimensions.—Diameter of the disk (with seven rings) 0.2; breadth of the rings 0.01 to 0.02; pores 0.002 to 0.01.

Habitat.—Pacific, central area, Stations 263 to 274, depth 2350 to 2925 fathoms.

10. Stylodictya setigera, Ehrenberg.

Stylodictya setigera, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiii. fig. 4.

Inner rings of the disk (two to three) convoluted in a simple or double spiral, outer rings (two to three) concentric, circular, or roundish. Breadth of the rings nearly equal. Pores regular, circular, three on the breadth of each ring. Marginal spines twenty to forty, bristle-shaped, about twice as long as the ring-breadth. (The specimen figured by Ehrenberg was a young one; in older specimens I found the inner spiral disk surrounded by two to three concentric circular rings.)

Dimensions.—Diameter of the disk (with six rings) 0.16; breadth of the rings 0.12; pores 0.003.

Habitat.—Fossil in the rocks of Barbados; also living in the depths of the Central Pacific, Station 266, depth 2750 fathoms.

Subgenus 3. Stylospira, Haeckel, 1862, Monogr. d. Radiol., p. 515.

Definition.—All rings of the disk convoluted in a simple or double spiral (sometimes also in quartered half-spirals).

11. Stylodictya heliospira, n. sp. (Pl. 41, fig. 8).

Stylospira heliospira, Haeckel, 1879, MS.

All rings of the disk convoluted in a simple regular spiral, increasing in breadth from the centre towards the periphery; the sixth ring twice as broad as the second. Pores irregular, roundish, two on the breadth of each ring. Marginal spines numerous, thirty to forty, bristle-shaped, nearly half as long as the radius of the disk.

Dimensions.—Diameter of the disk (with seven rings) 0.16; breadth of the inner rings 0.008, of the outer 0.016; pores 0.002 to 0.006.

Habitat.—Mediterranean, Portofino near Genoa, surface; also fossil in the Tertiary rocks of Sicily; Caltanisetta, Haeckel.

12. Stylodictya hertwigii, Haeckel.

Stylospira arachnia, R. Hertwig, 1879, Organismus d. Radiol., p. 59, Taf. vi. fig. 8.

All rings of the disk convoluted in a simple regular spiral, with increasing breadth from the centre; the fifth ring twice as broad as the second. Pores regular, circular, two on the breadth of each ring. Twelve piercing radial beams and some others interrupted, prolonged into twelve to twenty radial marginal spines, bristle-shaped, about as long as the diameter of the disk.

Dimensions.—Diameter of the disk (with five rings) 0.15; breadth of the second ring 0.01, of the fifth 0.02; pores 0.006.

Habitat.—Mediterranean (Messina), R. Hertwig.

13. Stylodictya dujardinii, Haeckel.

Stylospira dujardinii, Haeckel, 1862, Monogr. d. Radiol., p. 515, Taf. xxix. figs. 9, 10.

All rings of the disk convoluted in a simple regular spiral, of nearly equal breadth. Pores regular, circular, two on the breadth of each ring. Very numerous (twenty to thirty or more) piercing radial beams, prolonged into bristle-shaped marginal spines, about as long as the diameter of the disk.

Dimensions.—Diameter of the disk (with six rings) 0.12; breadth of each ring 0.01; pores 0.004.

Habitat.—Mediterranean (Messina), Haeckel.

14. Stylodictya echinastrum, Ehrenberg.

Stylodictya echinastrum, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiii. fig. 1.

All rings of the disk convoluted in a double spiral, of nearly equal breadth. Pores irregular, roundish, two to three on the breadth of each ring. Marginal spines numerous, twenty to thirty, of very different size, the largest conical, strong, about as long as the diameter of the disk, and on the base as broad as one ring.

Dimensions.—Diameter of the disk (with five rings) 0.12; breadth of each ring 0.01; pores 0.002 to 0.006.

Habitat.—Fossil in the rocks of Barbados.

15. Stylodictya clavata, Ehrenberg.

Stylodictya clavata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiii. fig. 2.

All rings of the disk convoluted in a half spiral, of nearly equal breadth; each ring by four zigzag beams (crossed in two perpendicular diameters) divided into four equal quarters; the spiral line of each quarter ring halving both neighbouring quarters. Pores regular, circular, two on the breadth of each ring. Eight marginal spines short, conical, with thin pedicle; four perradial (as prolongations of the four internal beams) alternating with four interradial spines arising from the margin of the disk.

Dimensions.—Diameter of the disk (with five rings) 0.13; breadth of each ring 0.014; pores 0.003.

Habitat.—Fossil in the rocks of Barbados.

Genus 222. Stylochlamydium,^[48] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with numerous (five or more, commonly eight to twelve) solid radial spines, regularly or irregularly disposed on the margin of the circular or polygonal disk; margin of the disk surrounded by a thin, porous (but not chambered), equatorial girdle.

The genus Stylochlamydium is intermediate between Perichlamydium (with which it was formerly united) and Stylodictya. It deals with the former in the peculiar equatorial girdle, with the latter in the radial spines of the disk margin, which pierce the girdle. To both these genera it shows slow transitions, and can hardly be subjected to a sharp definition.

Subgenus 1. Stylochlamys, Haeckel.

Definition.—All rings of the disk concentric, circular (or somewhat polygonal).

1. Stylochlamydium asteriscus, n. sp. (Pl. 41, fig. 10).

Perichlamydium asteriscus, Haeckel, 1879, MS.

All rings of the disk concentric, circular, or polygonal, with increasing breadth from the centre; the fifth ring twice as broad as the second. Pores irregular, roundish, three to four on the breadth of each ring; in the rings two to six times as large as in the equatorial girdle, which is half as broad or two-thirds as broad as the radius of the disk. Twelve bristle-shaped radial spines are connected by the girdle near to the points; four crossed spines arising from the central chamber; two others between these in each quadrant arising from the first ring.

Dimensions.—Diameter of the disk (with five rings) 0.15, with the girdle 0.25; breadth of the second ring 0.01, of the fifth ring 0.02; pores 0.001 to 0.005.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

2. Stylochlamydium limbatum, Haeckel.

Perichlamydium limbatum, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 43; Mikrogeol., 1854, Taf. xxii. fig. 20. Perichlamydium limbatum, Haeckel, 1862, Monogr. d. Radiol., p. 494.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, two on the breadth of each ring; twice to three times as large as the fine pores of the equatorial girdle, which is about half as broad as the radius of the disk. Twelve (or eleven) bristle-shaped radial spines are connected by the girdle near to the points, irregularly disposed.

Dimensions.—Diameter of the disk (with five rings) 0.12, with the girdle 0.2, breadth of each ring 0.01; pores 0.001 to 0.003.

Habitat.—Fossil in the Tertiary rocks of Sicily, Caltanisetta, Grotte.

3. Stylochlamydium venustum, Haeckel.

Perichlamydium venustum, Bailey, 1856, Amer. Journ., vol. xxii. p. 5, pl. i. figs. 16, 17. Perichlamydium venustum, Haeckel, 1862, Monogr. d. Radiol., p. 495.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, everywhere of nearly equal size, three on the breadth of each ring, a little smaller in the equatorial girdle, which is about as broad as the radius of the disk. Twenty to twenty-four bristle-shaped radial spines, irregularly disposed, proceed with their free points over the margin.

Dimensions.—Diameter of the disk (with four rings) 0.1, with the girdle 0.3; breadth of each ring 0.011; pores 0.002.

Habitat.—North Pacific, Kamtschatka, Bailey.

4. Stylochlamydium æquale, Haeckel.

Perichlamydium æquale, Stöhr, 1880, Palæontogr., vol. xxvi. p. 109, pl. v. fig. 2.

All rings of the disk concentric, circular, with increasing breadth from the centre; the sixth ring twice as broad as the second. Pores regular, circular, everywhere of equal size; on the breadth of the inner rings one, of the outer two, of the girdle three pores. Girdle only one-fourth as broad as the radius of the disk. About twenty bristle-shaped radial spines, irregularly disposed, are connected by the girdle near to the points.

Dimensions.—Diameter of the disk (with six rings) 0.11, with the girdle 0.17; breadth of the second ring 0.006, of the sixth 0.013; pores 0.006.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

Subgenus 2. Stylochlamyum, Haeckel.

Definition.—Rings of the disk all (or in part) not concentric, spirally convoluted or irregular.

5. Stylochlamydium perispirale, Haeckel.

Perichlamydium limbatum, var. Stöhr, 1880, Palæontogr., vol. xxvi. p. 109, Taf. v. fig. 1.

Inner rings of the disk concentric, circular, outer rings convoluted spirally, all rings of equal breadth. Pores regular, circular, two on the breadth of each ring, twice as large as in the equatorial girdle, which is about half as broad as the radius of the disk. Twelve to sixteen bristle-shaped radial spines, irregularly disposed, are connected by the girdle near to the points.

Dimensions.—Diameter of the disk (with six rings) 0.12, with the girdle 0.2; breadth of each ring 0.011; pores in the central disk 0.004, in the girdle 0.002.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

6. Stylochlamydium spongiosum, Haeckel.

Perichlamydium spongiosum, Stöhr, 1880, Palæontogr., vol. xxvi, p. 109, Taf. v. fig. 3.

Rings of the disk partly concentric, partly spiral, more or less irregular and often interrupted, with increasing breadth from the centre. Central part of the disk more or less spongy and obscure. Equatorial girdle half as broad as the radius of the chambered disk, with smaller pores than the latter, pierced by twenty to thirty thin, bristle-shaped radial beams, which proceed over the margin of the disk.

Dimensions.—Diameter of the disk (with ten rings) 0.2, with the girdle 0.3; breadth of the rings 0.005 to 0.015; pores 0.001 to 0.005.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms; also fossil in the Tertiary rocks of Barbados and Sicily.

Subfamily 5. Euchitonida, Haeckel.

Definition.—Porodiscida with two or more (commonly three or four) radial chambered or spongy arms on the margin of the concentrically annulated disk, situated in its equatorial plane (with or without a connecting patagium between the arms).

Genus 223. Amphibrachium,^[49] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with two simple, undivided, chambered arms, opposite in one axis, without a patagium.

The genus Amphibrachium opens the long series of the Euchitonida, or of those Porodiscida which bear on the margin of the circular central disk a certain number of chambered arms, composed of a series of chambers which are separated by transverse septa. The first group or tribe of this subfamily is formed by the Amphibrachida, in which the disk bears only two arms opposite on the poles of one axis. The simplest form of these is Amphibrachium, in which both arms are simple, equal, and without a patagium or spongy connecticulum.

Subgenus 1. Amphibrachella, Haeckel.

Definition.—Both arms equal, of the same form and size, blunt at the distal end, without a terminal spine.

1. Amphibrachium sponguroides, n. sp.

Both opposite arms of the same form and size, nearly cylindrical, three times as long as broad, with six to eight transverse septa or joints, at the distal end rounded, blunt, without a terminal spine.

Dimensions.—Radius of each arm 0.22, breadth 0.065.

Habitat.—Antarctic Ocean, Station 154, surface.

2. Amphibrachium lanceolatum, n. sp.

Both arms equal, lanceolate, in the middle part three times as broad as at the two ends, two and a half times as long as broad, with eight to nine transverse septa, at the distal end blunt, without a terminal spine.

Dimensions.—Radius of each arm 0.3, greatest breadth 0.09.

Habitat.—Pacific, central area, Station 267, depth 2700 fathoms.

3. Amphibrachium dilatatum, n. sp. (Pl. 44, fig. 6).

Both arms equal, trapezoidal, somewhat broader than long, on the convex distal end three times as broad as on the narrow base, with five to six transverse septa, without a terminal spine. Central disk large, somewhat irregular, with three to four rings, twice as broad as the base of the arms.

Dimensions.—Radius of each arm 0.32, basal breadth 0.15, terminal breadth 0.44.

Habitat.—South Atlantic, off Patagonia, Station 319, surface.

Subgenus 2. Amphibrachidium, Haeckel.

Definition.—Both arms equal, of the same size and form, with terminal spines.

4. Amphibrachium amphilonche, n. sp.

Both arms equal, lanceolate, in the middle part four times as broad as at the two ends, twice as long as broad; on the distal end of each arm is a long conical spine.

Dimensions.—Radius of each arm (without terminal spine) 0.2, breadth 0.08.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

5. Amphibrachium capitatum, n. sp.

Both arms equal, club-shaped, three times as long as broad, in the outer distal half thickened, three times as broad as at the narrow base; on the distal end of each arm a strong, angular, terminal spine. (The form of the arms like that of Stephanastrum capitatum, Pl. 44, fig. 1.)

Dimensions.—Radius of each arm 0.22, basal breadth 0.02, terminal breadth 0.06.

Habitat.—Equatorial Atlantic, Station 347, surface.

6. Amphibrachium armatum, n. sp.

Both arms equal, four times as long as broad, in the thickened distal part twice as broad as at the base, thorny, with twenty to thirty larger spines on the distal end, and a very large pyramidal spine in the longitudinal axis. (The form of the arms like that of the odd arm in Euchitonia carcinus, Pl. 43, fig. 10.)

Dimensions.—Radius of each arm 0.24, basal breadth 0.03, distal breadth 0.06.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

Subgenus 3. Amphibrachoma, Haeckel.

Definition.—Both arms of different size or form, without terminal spines.

7. Amphibrachium indicum, n. sp.

Both arms club-shaped, but very different in size and form; larger arm three times as long and twice as broad as the smaller arm; the larger with nine joints slowly increasing in size, the smaller with four joints, rapidly increasing; the terminal joint three times as broad as the basal. Distal end blunt, rounded, without spines.

Dimensions.—Radius of the larger arm 0.24, of the smaller 0.08; distal breadth of the former 0.06, of the latter 0.03; basal breadth 0.015.

Habitat.—Indian Ocean, Ceylon, Haeckel, surface.

Subgenus 4. Amphibrachura, Haeckel.

Definition.—Both arms of different size or form, with terminal spines.

8. Amphibrachium clavula, n. sp.

Both arms different in size and form; larger arm club-shaped, four times as long as broad, at the distal end three times as broad as at the base, and twice as long as the smaller arm, which resembles a stalked knob, with thin basal peduncle and spherical distal part. Ends of the two arms thorny (with numerous smaller, and three to five larger spines); one very large conical terminal spine on each pole of the main axis.

Dimensions.—Radius of the larger arm 0.3, of the smaller 0.15; distal breadth of the former 0.06, of the latter 0.04; basal breath 0.02.

Habitat.—South Atlantic, Station 333, surface.

Genus 224. Amphymenium,^[50] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with two simple, undivided, chambered arms, opposite in one axis, connected by a patagium.

The genus Amphymenium differs from the preceding Amphibrachium, its ancestral form, by development of a patagium or connecticulum between both arms. This forms a latticed or more spongy envelop, which surrounds either the middle part of the shell, or the whole shell with exception of the distal ends of both arms. If the envelop become very spongy, the shell may be confounded with the cylindrical Ellipside Spongocore (nearly allied to Spongurus); possibly also Ommatogramma of Ehrenberg belongs to this genus.

Subgenus 1. Ommatogramma, Ehrenberg (?).

Definition.—Both opposite arms of the same size and form, blunt, without terminal spines.

1. Amphymenium pupula, n. sp. (Pl. 44, fig. 8).

Both arms equal, twice as long as broad, three-jointed; the terminal joint egg-shaped, as large as both other joints together; distal end rounded, blunt. Patagium nearly complete, enveloping the arms with exception of the distal end. Perimeter nearly spindle-shaped.

Dimensions.—Radius of each arm 0.17, greatest breadth 0.06; transverse breadth of the patagium 0.13.

Habitat.—Pacific, central area, Station 273, depth 2350 fathoms.

2. Amphymenium naviculare, Haeckel.

? Ommatogramma navicularis, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 317; Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. vi. fig. 7.

Both arms equal, three times as long as broad, spongy, not jointed; distal end a little club-shaped, blunt. Patagium nearly complete, enveloping the arms with exception of the distal end. Perimeter nearly lanceolate. The imperfect diagnosis and figure of Ehrenberg make it doubtful whether this species belongs to the Porodiscida (Amphymenium) or to the Spongodiscida (Spongobrachium) or perhaps to the Spongurida (Spongocore).

Dimensions.—Radius of each arm 0.1, greatest breadth 0.03; transverse breadth of the patagium 0.05.

Habitat.—North Pacific, Californian Sea, depth 2600 fathoms, Ehrenberg.

3. Amphymenium zygartus, n. sp. (Pl. 44, fig. 7).

Both arms equal, four times as long as broad, with seven to eight joints, slowly decreasing in size towards the blunt end. Patagium incomplete, protecting only the middle part of the shell on both sides; on each side two parallel lattice-plates, connected by transverse radial beams, perpendicular to the surface. Perimeter nearly rectilinear. (Resembles much certain forms of Zygartus, Pl. 40, but is a true Discoid, no Prunoid.) Compare also Pl. 45, fig. 8.

Dimensions.—Radius of each arm 0.2, greatest breadth 0.05; transverse breadth of the patagium 0.11.

Habitat.—Pacific, central area, Station 271, surface.

4. Amphymenium monstrosum, n. sp. (Pl. 44, fig. 11).

Both arms equal, little longer than broad, with six to seven convex joints. The axis of both arms is not common and straight, as in all other species of this genus, but broken, therefore the incomplete patagium, which envelops only two to three joints of the arms, is on one side convex, on the other side concave; it is formed by a simple lattice-plate, connected with the arms by numerous radial beams. This anomalous form, seen only once, may perhaps be a monstrosity of Euchitonia.

Dimensions.—Radius of each arm 0.12, greatest breadth 0.06; transverse breadth of the patagium 0.13.

Habitat.—South Pacific, Station 290, surface.

Subgenus 2. Ommathymenium, Haeckel.

Definition.—Both opposite arms of the same size and form, armed at the distal end with terminal spines.

5. Amphymenium amphistylium, n. sp. (Pl. 44, fig. 9).

Both arms equal, three times as long as broad, thickened towards the truncated distal end, and armed with a strong pyramidal terminal spine. Each arm with seven joints, separated by convex, transverse septa, and halved by a radial beam lying in the longitudinal axis. Patagium incomplete, cylindrical, enveloping only the middle part of the shell.

Dimensions.—Radius of each arm 0.18, greatest breadth 0.06; transverse breadth of the patagium 0.08.

Habitat.—North Atlantic, Station 354, surface.

6. Amphymenium fusiforme, n. sp.

Both arms equal, lanceolate, three times as long as broad in the width, with seven to eight joints. Distal end pointed, armed with a strong conical terminal spine. Patagium complete, enveloping the whole shell with exception of the terminal spines. Whole form spindle-shaped.

Dimensions.—Radius of each arm 0.2, greatest breadth 0.07; transverse breadth of the patagium 0.15.

Habitat.—South Atlantic, Station 330, surface.

Genus 225. Amphirrhopalum,^[51] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with two chambered arms, opposite in one axis, without a patagium; one arm or both forked at the distal end.

The genus Amphirrhopalum differs from Amphibrachium, its ancestral form, by bifurcation of the distal ends of the arms, which may affect either both arms, or only one of them.

Subgenus 1. Amphirrhopalium, Haeckel.

Definition.—Both opposite arms of similar size and form, with blunt branches, without terminal spines.

1. Amphirrhopalum ximorphum, n. sp.

Both arms equal, in the proximal half simple, in the distal half forked, with six to seven transverse septa; distal end of each branch blunt, without terminal spine, somewhat broader than the base of the whole arm. Axis of the branches concavely curved. (Resembles Amphicraspedum maclaganium, Pl. 45, fig. 11, but wants the patagium.)

Dimensions.—Radius of the arms 0.18, basal breadth 0.065; terminal breadth of each branch 0.075.

Habitat.—North Pacific, off Japan, Station 240, surface.

2. Amphirrhopalum amphidicranum, n. sp.

Both arms equal, in the proximal half simple, in the distal half forked, with irregular septa; distal end of each arm blunt, without a terminal spine, smaller than the basal breadth of the arm. Axis of the branches straight. (Resembles Dicranastrum furcatum, Pl. 47, fig. 2, but without lateral arms.)

Dimensions.—Radius of each arm 0.15, basal breadth 0.03; terminal breadth of each branch 0.02.

Habitat.—Pacific, central area, Station 263, depth 2650 fathoms.

Subgenus 2. Amphirrhopella, Haeckel.

Definition.—Both opposite arms of similar size and form, with terminal spines.

3. Amphirrhopalum bigeminum, n. sp.

Both arms equal, in the proximal larger half simple, in the distal smaller half forked; each branch triangular, with a strong conical terminal spine. Axis of the branches straight. (Resembles Dicranastrum cornutum, Pl. 45, fig. 2, but without lateral arms.)

Dimensions.—Radius of the arms (without spines) 0.15, basal breadth 0.03; breadth of the bifurcation 0.08.

Habitat.—South Pacific, Station 284, surface.

4. Amphirrhopalum echinatum, n. sp. (Pl. 45, fig. 10).

Both arms equal, in the proximal smaller half simple, nearly square, in the distal larger half forked; the branches thorny, armed at the end with numerous spines, one larger on the terminal pole of the concavely curved arm-axis.

Dimensions.—Radius of the arms (without spines) 0.15, basal breadth 0.05; breadth of branches 0.03.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

Subgenus 3. Amphirrhopoma, Haeckel.

Definition.—Both opposite arms of different size or form, without terminal spines.

5. Amphirrhopalum ypsilon, n. sp.

Both arms very different. Larger arm simple, egg-shaped, twice as long as broad; smaller arm in the basal half simple, nearly square, in the distal half forked; both branches egg-shaped, blunt. (Resembles Amphicraspedum wyvilleanum, Pl. 45, fig. 12, but wants the patagium.)

Dimensions.—Radius of the larger simple arm 0.18, breadth 0.09; radius of the smaller forked arm 0.15, breadth of its branches 0.05.

Habitat.—Indian Ocean, Madagascar, Rabbe, surface.

Genus 226. Amphicraspedum,^[52] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with two chambered arms, opposite in one axis, connected by a lateral patagium; one arm or both forked at the distal end.

The genus Amphicraspedum exhibits the same bifurcation of the arms as does Amphirrhopalum, but differs from this ancestral form in the development of a patagium, an external connecticulum between the arms, which envelops the disk totally or partially.

Subgenus 1. Amphicraspedon, Haeckel.

Definition.—Both arms of equal size and form, without terminal spines of the branches.

1. Amphicraspedum maclaganium, n. sp. (Pl. 45, fig. 11).

Both arms equal, in the proximal half simple, in the distal half forked, with six to seven transverse septa; distal end of each branch rounded, blunt, somewhat broader than the base of the whole arm. Divergent axes of both branches concavely curved. Patagium incomplete, with elliptical perimeter, enveloping only the middle part of the shell. I call this interesting species in honour of Miss Nellie Maclagan, the learned translator of several zoological papers from German into English.

Dimensions.—Radius of each arm 0.25, basal breadth 0.07; distal breadth of each branch 0.08; equatorial breadth of the patagium 0.25.

Habitat.—North Atlantic, off Halifax, Station 50, surface.

Subgenus 2. Amphicraspedina, Haeckel.

Definition.—Both arms of different size or form, without terminal spines on the branches.

2. Amphicraspedum wyvilleanum, n. sp. (Pl. 45, fig. 12).

Both arms different. Larger arm simple, egg-shaped, with eleven convex joints, one and a half times as long as broad; smaller arm in the basal half simple, triangular, with six cap-like joints, in the distal half forked; both branches egg-shaped, with five joints and blunt ends. Patagium nearly complete with four to five concave chamber-rows. Called in honour of Sir C. Wyville Thomson.

Dimensions.—Radius of the larger simple arm 0.18, breadth 0.08; radius of the smaller forked arm 0.16; breadth of the branches 0.05; transverse breadth of the patagium 0.2.

Habitat.—South Atlantic, Station 333, surface.

Subgenus 3. Amphicraspedula, Haeckel.

Definition.—Both arms of different size or form, with terminal spines of the branches.

3. Amphicraspedum murrayanum, n. sp. (Pl. 44, fig. 10).

Amphymenium murrayanum, Haeckel, 1879, MS. et Atlas (pl. xliv. fig. 10).

Both arms different in size; the larger one and a half times as long and broad as the smaller. Both arms triangular, forked at the broader distal end, with two very strong, conical, divergent, straight terminal spines. Patagium broad, incomplete, with circular perimeter. Called in honour of my friend Dr. John Murray.

Dimensions.—Radius of the larger arm (including the spines) 0.24, of the smaller 0.16; distance of the terminal points of the former 0.18, of the latter 0.09; diameter of the patagium 0.2.

Habitat.—North Atlantic, Færöe Channel, Gulf Stream, surface, John Murray.

Genus 227. Dictyastrum,^[53] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 830.

Definition.—Porodiscida with three simple, undivided, chambered arms, without a patagium; triangular shell regular, with three equal arms and three equal angles.

The genus Dictyastrum is the simplest form of the Trigonastrida, or of the Porodiscida, in which the margin of the central disk is furnished with three chambered arms. In Dictyastrum these are quite simple and regular, without a patagium, separated by equal angles, so that the whole shell represents a regular, equilateral triangle, if we connect the distal points of the arms by lines. The genus Dictyastrum, founded by Ehrenberg in 1860, differs from his Rhopalodictyum—after his own diagnosis—only by an insignificant difference in the form of the simple arms, which is scarcely a specific character. I therefore apply this name here in the above amended sense, seeing that the only figured species of Ehrenberg (Dictyastrum angulatum) occurs in two different, but externally very similar forms: one of these is a true Porodiscid (Dictyastrum) with two porous covering-plates and concentric rings; the other is a true Spongodiscid (Rhopalodictyum) with quite spongy, irregular network, and is probably identical with the Rhopalodictyum truncatum of Ehrenberg.

Subgenus 1. Dictyastrella, Haeckel.

Definition.—Arms with blunt ends, without terminal spines.

1. Dictyastrum angulatum, Ehrenberg.

Dictyastrum angulatum, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 289, Taf. viii. fig. 18.

Arms nearly square with straight edges, towards the truncated end a little broader, about the same diameter as the triangular central disk. The figure of Ehrenberg seems to represent a Spongodiscid (Rhopalodictyum angulatum), but in the same locality (Philippine Sea) occurs also a true Dictyastrum of quite the same form, but with three to four concentric rings of the central disk, and with jointed arms.

Dimensions.—Radius of each arm (length from the centre to the distal end) 0.13; breadth of the truncated end 0.1.

Habitat.—Tropical Pacific, Philippine Sea, Station 200, depth 250 fathoms.

2. Dictyastrum bandaicum, Haeckel.

Rhopalastrum bandaicum, Harting, 1863, Mikr. Fauna Banda-Zee, p. 16, Taf. iii. fig. 45.

Arms nearly square, with convex edges, in the middle a little broader than at both ends, about half the diameter of the central disk. Differs from the nearly allied preceding species by the half size of the arms and the convex edges.

Dimensions.—Radius of each arm 0.12, its greatest breadth 0.07.

Habitat.—Tropical Pacific, Banda Sea, Harting.

3. Dictyastrum hexagonum, n. sp. (Pl. 43, fig. 7).

Rhopalastrum hexagonum, Haeckel, 1880, Atlas (pl. xliii. fig. 1).

Arms nearly triangular, one and a third times as broad at the distal end as long, and three times as broad as at the base. Central disk about the same diameter. In each arm six simple broad chambers. If we connect the six corners of the truncated distal ends by straight lines, we get a regular hexagon.

Dimensions.—Radius of each arm 0.17, basal breadth 0.06, terminal breadth 0.17.

Habitat.—Equatorial Atlantic, Station 347, surface.

4. Dictyastrum trirrhopalum, n. sp.

Arms club-shaped, five times as long as broad at the base, at the thickened end three times as broad as at the base. Diameter of the central disk equals half the length of the arms. (Similar to Rhopalastrum malleus, Pl. 43, fig. 1, but with three equal angles and much smaller disk.)

Dimensions.—Radius of each arm 0.25, basal breadth 0.04, distal breadth 0.12.

Habitat.—Pacific, central area, Station 273, surface.

Subgenus 2. Dictyastromma, Haeckel.

Definition.—Arms on the distal end provided with terminal spines.

5. Dictyastrum trispinosum, n. sp. (Pl. 43, fig. 5).

Rhopalastrum trispinosum, Haeckel, 1881, Prodromus et Atlas (pl. xliii. fig. 5).

Arms trapezoid, at the rounded distal end twice as broad as at the base, with a strong and short, conical, terminal spine. Diameter of the circular central disk about equal to the length and the greatest breadth of the arms.

Dimensions.—Radius of each arm 0.15, basal breadth 0.06, distal breadth 0.11.

Habitat.—Equatorial Atlantic, Station 347, surface.

6. Dictyastrum triactis, Ehrenberg.

Dictyastrum triactis, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 306.

Arms rectilinear, four times as long as broad, with parallel edges, pointed at the distal end, with a short terminal spine. Diameter of the circular central disk equal to double the breadth of the arms.

Dimensions.—Radius of each arm 0.2, breadth 0.04.

Habitat.—Pacific, Philippine Sea, Station 206, depth 2100 fathoms.

7. Dictyastrum aculeatum, n. sp.

Arms lanceolate, three times as long as broad, twice as broad in the middle as at either end, with thorny surface and numerous conical terminal spines, one very large in the radius. Central disk triangular, about as broad as the arms. (Resembles Rhopalastrum arcticum, Pl. 43, fig. 6, but differs by the equal angles and the triangular disk.)

Dimensions.—Radius of each arm 0.2, breadth 0.06.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

Genus 228. Rhopalastrum,^[54] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Porodiscida with three simple undivided, chambered arms, without a patagium; triangular shell bilateral, one odd arm opposite to the odd angle between two paired arms.

The genus Rhopalastrum, founded by Ehrenberg (1847) with a very insufficient diagnosis, is here retained for those Trigonastrida that agree in the generic characters with the only species figured by him, viz., Rhopalastrum lagenosum (compare my Monograph, 1862, p. 500). It comprises, therefore, such Euchitonida as agree with the preceding Dictyastrum in the simple form of the three arms and the absence of a patagium, but differ from it in the different size of the three angles, and often also in the divergent form and size of the three arms; one odd arm is opposite to the odd angle between the two paired arms.

Subgenus 1. Rhopalastrella, Haeckel.

Definition.—Arms with blunt ends, without terminal spines.

1. Rhopalastrum truncatum, Haeckel.

Rhopalastrum truncatum, Haeckel, 1862, Monogr. d. Radiol., p. 500, Taf. xxix. fig. 6.

Distance of both paired arms about half as large as their distance from the odd arm. All three arms nearly of the same form and size, very short and broad; their breadth nearly equals that of the roundish central disk, whilst their length reaches only one-fourth of it. End of the arms convex rounded, without spines.

Dimensions.—Radius of each arm 0.1, breadth 0.15.

Habitat.—Mediterranean (Messina), Atlantic (Canary Islands), surface, Haeckel.

2. Rhopalastrum pistillum, Stöhr.

Rhopalastrum pistillum, Stöhr, 1880, Palæontogr., vol. xxvi. p. 110, Taf. v. fig. 4.

Distance between the paired arms about two-thirds as large as their distance from the odd arm. All three arms nearly of the same form and size, about three times as long as the diameter of the central disk, at the base one-third as broad as at the convex rounded end, without spines. Stöhr has only observed a fragment with one arm; some perfect specimens, which I found in the Caltanisetta-rock, exhibited nearly the same form as Rhopalastrum malleus (Pl. 43, fig. 1), but differ from this by the smaller disk, the broader arms, and the smaller angle between the paired arms.

Dimensions.—Radius of all three arms 0.2; basal breadth of each arm 0.045, terminal breadth 0.13.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Haeckel).

3. Rhopalastrum malleus, n. sp. (Pl. 43, fig. 1).

Distance between the paired arms one and a third times as large as their distance from the odd arm. All three arms nearly of the same form and size, hammer-shaped, three times as broad at the truncated distal end as at the base. Central disk broader than the arms.

Dimensions.—Radius of each arm 0.25, basal breadth 0.05, distal breadth 0.15.

Habitat.—South Atlantic, Station 325, surface.

4. Rhopalastrum lagenosum, Ehrenberg.

Rhopalastrum lagenosum, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 43; Mikrogeol., 1854, Taf. xxii. fig. 22.

Rhopalastrum lagenosum, Haeckel, 1862, Monogr. d. Radiol., p. 501.

Flustrella bilobata, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 81.

Haliomma lagena, Ehrenberg, 1840, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 200.

Distance between the paired arms one and a half times as great as their distance from the odd arm. All three arms nearly of the same form and size, about one and a half times as long as the diameter of the central disk, at the base half as broad as at the convex rounded end, without spines. Ehrenberg has only observed a fragment with two paired arms; some perfect specimens with three arms, observed by me, differed from the nearly allied Rhopalastrum pistillum (from the same locality) by the larger disk, the broader arms, and the larger unpaired angle.

Dimensions.—Radius of all three arms 0.2, basal breadth 0.05, terminal breadth 0.09.

Habitat.—Fossil in Tertiary rocks of Sicily, Caltanisetta.

5. Rhopalastrum ypsilinum, n. sp. (Pl. 43, fig. 2).

Distance between the paired arms half as large as their distance from the odd arm. All three arms at the concavely curved distal end three times as broad as at the narrow base. Odd arm twice as long and broad as the paired arms. Central disk smaller than the latter. No terminal spines.

Dimensions.—Radius of the odd arm 0.32, of the paired arms 0.2; terminal breadth of the former 0.2, of the latter 0.12.

Habitat.—Indian Ocean, Cocos Islands, Rabbe, surface.

6. Rhopalastrum clavatum, n. sp.

Distance between the paired arms half as large as their distance from the odd arm. All three arms club-shaped, at the thickened, nearly spherical, distal end three times as broad as at the narrow base. Odd arm nearly twice as long and broad as the paired arms. Central disk equal to the distal knob of the latter. No terminal spines.

Dimensions.—Radius of the odd arm 0.3, of the paired arms 0.18; distal breadth of the former 0.16, of the latter 0.08.

Habitat.—South Atlantic, Station 332, surface.

7. Rhopalastrum irregulare, n. sp. (Pl. 43, fig. 8).

Distance between all three arm-points different. All three arms cylindrical, nearly of the same length, but of different form, irregularly curved, about four times as long as broad, with blunt ends.

Dimensions.—Length of each arm about 0.2, breadth 0.05.

Habitat.—Antarctic Sea, Station 157, depth 1950 fathoms.

Subgenus 2. Rhopalastromma, Haeckel.

Definition.—Arms on the distal end provided with one or more terminal spines.

8. Rhopalastrum martellum, n. sp.

Distance between all three arm-points nearly the same; but the odd arm is one and a half times as large as both paired arms, and is perpendicular to the common axis of the latter, therefore the shell has the form of a hammer. Each arm is twice as broad at the distal end as at the base, and armed with a conical terminal spine; the latter is vertical in the odd arm, horizontal in the paired arms.

Dimensions.—Radius of the odd arm 0.3, of the paired arms 0.15; distal breadth of the former 0.12, of the latter 0.06.

Habitat.—North Atlantic, Station 354, surface.

9. Rhopalastrum triceros, n. sp. (Pl. 43, fig. 4).

Distance between the paired arms about two-thirds as large as their distance from the odd arm. All three arms club-shaped, three times as broad at the thickened distal part as at the base, and armed with one single, conical, terminal spine. Odd arm of the same breadth, but twice as long as the paired arms.

Dimensions.—Radius of the odd arm 0.35, of the paired arms 0.2; basal breadth 0.04, distal breadth 0.12.

Habitat.—Pacific, central area, Station 274, surface.

10. Rhopalastrum hexaceros, n. sp. (Pl. 43, fig. 3).

Distance between the paired arms equals four-fifths of their distance from the odd arm. All three arms nearly of the same size, about square, a little broader at the truncated distal end, which is armed at both corners with a strong, conical, radial spine.

Dimensions.—Radius of each arm 0.2, basal breadth 0.1, distal breadth 0.12.

Habitat.—Indian Ocean, Ceylon, Belligemma, Haeckel, surface.

11. Rhopalastrum arcticum, n. sp. (Pl. 43, fig. 6).

Distance between the paired arms half as large as their distance from the odd arm, which is a little larger. All three arms of the same form, lanceolate, twice to three times as long as broad, twice as broad in the middle as at either end. Each arm with twelve to fourteen transverse septa, at the distal end with a bunch of conical spines, and one single, very large, pyramidal, terminal spine.

Dimensions.—Radius of each arm (without spine) 0.17, greatest breadth of it 0.05 to 0.06.

Habitat.—Arctic Ocean, lat. 83° 19' N., North Polar expedition of the "Alert."

Genus 229. Hymeniastrum,^[55] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Porodiscida with three simple, undivided, chambered arms, connected by a patagium; triangular shell regular, with three equal arms and three equal angles.

The genus Hymeniastrum was founded by Ehrenberg (1847) with a very incomplete diagnosis, and hitherto known only by one single species, figured by him as Hymeniastrum pythagoræ (Mikrogeol., 1854, Taf. xxxvi. fig. 31). This form occurs in two different states, externally quite identical; in one state the central disk (as figured, loc. cit.), is a simple lens or hollow disk, containing a medullary shell or "central chamber"; in the other state the central disk is composed of two concentric rings surrounding the "central chamber." We retain here the name Hymeniastrum for this latter state, expressed in the diagnosis given above, and call the former state (the Coccodiscid) Hymenactura (compare above, p. 473). One practical advantage, obtained in this way, is that all genera of Discoidea ending with "-astrum" belong to the Porodiscida. Hymeniastrum differs from Dictyastrum by the possession of a patagium, and from Euchitonia by the equal size of the angles and the arms.

Subgenus 1. Hymenastrella, Haeckel.

Definition.—Arms with blunt ends, without terminal spines.

1. Hymeniastrum leydigii, Haeckel.

Euchitonia leydigii, Haeckel, 1862, Monogr. d. Radiol., p. 510, Taf. xxxi. figs. 4, 5.

Hymeniastrum leydigii, Haeckel, 1881, Prodromus, p. 460.

Histiastrum trinacrium, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 843.

Arms twice as long as broad, two-thirds as broad at the base as at the blunt, nearly truncated distal end. Patagium nearly complete, perfectly filling out the interbrachial spaces, with six to seven regular, concave chamber-rows; only the truncate terminal faces of the arms free.

Dimensions.—Radius of the arms 0.15 to 0.18, breadth on their base 0.04 to 0.05, on their broadest distal end 0.06 to 0.07.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface. Very common and variable.

2. Hymeniastrum köllikeri, Haeckel.

Euchitonia köllikeri, Haeckel, 1862, Monogr. d. Radiol., p. 511, Taf. xxxi. figs. 6, 7. Hymeniastrum köllikeri, Haeckel, 1881, Prodromus, p. 460.

Arms nearly lanceolate, twice as long as broad, half as broad at the base as at the broadest middle part, pointed at the distal end. Patagium complete, enveloping the whole triangular disk, with irregular chamber-rows.

Dimensions.—Radius of the arms 0.2, breadth on their base 0.04, on the broadest part 0.08.

Habitat.—Mediterranean (Messina), surface.

3. Hymeniastrum gümbelii, Haeckel.

Stylactis gümbelii, Stöhr, 1880, Palæontogr., vol. xxvi. p. 112, Taf. vi. fig. 1.

Arms twice as long as broad, nearly twice as broad in the circular distal half as in the square proximal half. Patagium incomplete, circular, with eight to nine convex chamber-rows, enveloping only the proximal square halves of the arms; the lenticular distal halves remain free.

Dimensions.—Radius of the arms 0.14; breadth at the base 0.04, at the distal lenticular part 0.07.

Habitat.—Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.

4. Hymeniastrum euclidis, n. sp. (Pl. 43, fig. 13).

Euchitonia euclidis, Haeckel, 1881, Prodromus, p. 460 et Atlas (pl. xliii. fig. 13).

Arms one and a half times as long as broad, club-shaped, three times as broad in the oval distal part as in the narrow square proximal part. Patagium complete, enveloping the whole triangular disk, and also the convex ends of the arms, with eight to nine convex chamber-rows.

Dimensions.—Radius of the arms 0.18; breadth at the base 0.025, at the broadest distal part 0.07.

Habitat.—Pacific, central area, Stations 270 to 274, surface.

5. Hymeniastrum pythagoræ, Ehrenberg.

Hymeniastrum pythagoræ, Ehrenberg, 1854 (partim), Mikrogeol., Taf. xxxvi. fig. 31.

Arms nearly as broad as long, two-thirds as broad at the base as at the truncated distal end. Patagium incomplete, enveloping only the basal half of the arms, with four to five rectilinear parallel chamber-rows. (This form has the greatest resemblance to the figure given by Ehrenberg, loc. cit., but differs by the central disk, which is composed of two concentric rings surrounding the small central chamber; compare above Hymenactura pythagoræ, p. 474.)

Dimensions.—Radius of the arms 0.18; breadth at the base 0.08, at the truncated end 0.12.

Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.

6. Hymeniastrum archimedis, n. sp.

Arms nearly triangular, at the truncated, slightly convex end three times as broad as at the narrow base and one and a third times as broad as long; each arm with six simple chambers. Patagium incomplete, enveloping only the basal half of the arms with three to four convex chamber-rows. (Differs from Rhopalastrum hexagonum, Pl. 43, fig. 7, only by the patagium.)

Dimensions.—Radius of the arms 0.2; breadth at the base 0.07, at the truncated end 0.2.

Habitat.—Pacific, central area, Station 274, surface.

Subgenus 2. Hymenastromma, Haeckel.

Definition.—Arms at the distal end provided with radial spines.

7. Hymeniastrum ternarium, Haeckel.

Histiastrum ternarium, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 76, Taf. xxiv. fig. 2.

Arms two and a half times as long as broad, three times as broad at the truncated end as at the narrow base, with a strong, conical, radial spine at the end. Patagium incomplete, enveloping only the basal half of the arms, with three to four convex chamber-rows.

Dimensions.—Radius of the arms (without terminal spine) 0.02; breadth at the base 0.025, at the broadest terminal part 0.08.

Habitat.—Fossil in the rocks of Barbados.

8. Hymeniastrum trigonarium, n. sp.

Arms one and a half times as long as broad, a little broader at the rounded end than at the base, with three strong conical radial spines, one larger (in the radius of each arm) and two smaller on both sides of this. Patagium complete, with four to five rectilinear parallel chamber-rows, enveloping the whole arms (with exception of the terminal spines) and forming a perfect equilateral triangle.

Dimensions.—Radius of the arms (without terminal spines) 0.18; breadth at the base 0.1, at the distal part 0.12.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

Genus 230. Euchitonia,^[56] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 831 (sensu emendato).

Definition.—Porodiscida with three simple, undivided, chambered arms, connected by a patagium; triangular shell bilateral, one odd arm opposite to the odd angle between the two paired arms.

The genus Euchitonia, quite insufficiently characterised by Ehrenberg, was founded by him (1860) for one single species, afterwards (1872) described and figured as Euchitonia furcata. Retaining this species correctly as the type of this genus, I give to it here the above diagnosis. In my Monograph (1862, p. 503) I described seven Mediterranean species of Euchitonia. Three of these have in common the characters according to the present diagnosis: Euchitonia mülleri, Euchitonia virchowii, Euchitonia beckmanni; two others appertain (on account of the regular, not bilateral form) to Hymeniastrum, and two others (on account of the forked, not simple arms) to Trigonastrum. Afterwards (1880) three true fossil species of Euchitonia were described by Stöhr (Euchitonia cruciata, Euchitonia zittelii, and Euchitonia acuta). Some species of this genus are cosmopolitan, and appertain to the most common and everywhere represented Discoidea.

Subgenus 1. Stylactis, Ehrenberg, 1872 (loc. cit.).

Definition.—Arms with blunt ends, without terminal spines.

1. Euchitonia furcata, Ehrenberg.

Euchitonia furcata, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 308; Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. vi. iii. fig. 6.

Distance between the paired arms about half as large as their distance from the odd arm. All three arms nearly of the same size and form, about twice as long as broad, one and a half times at the blunt convex end as broad as at the base. Patagium incomplete, with concave chamber-rows and irregular network, only enveloping the basal half of the arms.

Dimensions.—Radius of all three arms 0.15, basal breadth of each arm 0.04, terminal breadth 0.06.

Habitat.—North Pacific, Californian Sea, depth 2600 fathoms, Ehrenberg.

2. Euchitonia mülleri, Haeckel.

Euchitonia mülleri, Haeckel, 1862, Monogr. d. Radiol., p. 508, Taf. xxx. figs. 5-10. Euchitonia mülleri, Stöhr, 1880, Palæontogr., vol. xxvi. p. 110, Taf. v. fig. 5.

Distance between the paired arms about two-thirds as large as their distance from the odd arm, which is somewhat larger. Length of the arms equals two and a half times the breadth of the blunt convex end or five times the breadth of the base. Patagium with concave chamber-rows, nearly complete, enveloping the arms with exception of the terminal face. (This common species is very variable; compare my Monograph.)

Dimensions.—Radius of all three arms 0.16 to 0.22, basal breadth 0.03 to 0.05, terminal breadth 0.06 to 0.08.

Habitat.—Cosmopolitan; one of the most common Discoidea in all seas, on the surface as well as at different depths; also fossil in the Tertiary rocks of Barbados and Sicily.

3. Euchitonia triangulum, Haeckel.

Stylactis triangulum, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 320; Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. viii. fig. 9. Stylactis triangulum, Stöhr, 1880, Palæontogr., vol. xxvi. p. 113, Taf. vi. fig. 2.

Distance between the paired arms about two-thirds as large as their distance from the odd arm. All three arms nearly of the same size and form, about one and a half times as long as broad, nearly as broad at the base as at the blunt rounded end. Patagium incomplete, with convex chamber-rows, enveloping about two-thirds of the arms.

Dimensions.—Radius of all three arms 0.15, basal breadth 0.05, terminal breadth 0.06.

Habitat.—Pacific and Atlantic, Stations 253, 272, 354, surface; also fossil in the Tertiary rocks of Barbados and Sicily.

4. Euchitonia cruciata, Stöhr.

Euchitonia cruciata, Stöhr, 1880, Palæontogr., vol. xxvi. p. 111, Taf. v. fig. 7.

Distance between the paired arms about one and a half times as large as their distance from the odd arm, which is a little larger. Length of the arm nearly equals twice the breadth, which is the same at the base and at the rounded blunt ends. Patagium incomplete, with concave chamber-rows, enveloping only the base of the arms, and forms between them three other smaller arms; therefore the whole shell forms six angles with six alternating arms.

Dimensions.—Radius of all three arms 0.15, basal breadth 0.05.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

5. Euchitonia lanceolata, n. sp. (Pl. 43, fig. 9).

Distance between the paired arms about one and a third times as large as their distance from the odd arm. All three arms nearly of the same size and form, three times as long as broad, lanceolate, much broader in the middle part than at both ends; distal end cuspidate, but not spiny. Patagium incomplete, with convex chamber-rows, envelops about two-thirds of the arms.

Dimensions.—Radius of all three arms 0.18, greatest breadth (in the width) 0.06.

Habitat.—North Atlantic, Station 353, depth 2965 fathoms.

6. Euchitonia zittelii, Haeckel.

Stylactis zittelii, Stöhr, 1880, Palæontogr., vol. xxvi. p. 112, Taf. v. fig. 8.

Distance between the paired arms about one-fifth as large as their distance from the odd arm. All three arms nearly of the same size and form, in the proximal half thinner and nearly square, in the distal half thicker and circular; the latter half twice to three times as broad as the former. Patagium incomplete, with convex chamber-rows, envelops only the proximal square half of the arms.

Dimensions.—Radius of all three arms 0.15, basal breadth 0.03, terminal breadth 0.08.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

7. Euchitonia stöhrii, n. sp. (Pl. 43, fig. 12).

Distance between the paired arms about four-fifths as large as their distance from the odd arm, which is one and a half times as long as the former. Arms about three times as long as broad, twice as broad in the distal half as in the proximal half, with rounded blunt ends. Patagium complete, with concave chamber-rows, enveloping the whole shell, also the ends of the arms.

Dimensions.—Radius of the paired arms 0.2, of the odd arm 0.25; basal breadth 0.03, distal breadth 0.06.

Habitat.—Fossil in the rocks of Barbados and of Nicobar Islands, Haeckel. Indian Ocean, Cocos Islands (Rabbe). Also in the Central Pacific, Station 267.

8. Euchitonia beckmannii, Haeckel.

Euchitonia beckmannii, Haeckel, 1862, Monogr. d. Radiol., p. 505, Taf. xxxi. fig. 1.

Distance between the paired arms scarcely half as large as their distance from the odd arm, which is somewhat larger. Each arm with six simple broad chambers (without radial septa), the terminal chambers semilunar, convex, blunt, four times as broad as the first (basal) chamber. Patagium incomplete, with convex chamber-rows, enveloping the arms with exception of the broad blunt terminal face.

Dimensions.—Radius of the paired arms 0.15, of the odd arm 0.18; basal breadth 0.02 to 0.03, terminal breadth 0.1 to 0.15.

Habitat.—Mediterranean (Messina), Haeckel, surface.

9. Euchitonia virchowii, Haeckel.

Euchitonia virchowii, Haeckel, 1862, Monogr. d. Radiol., p. 503, Taf. xxx. figs. 1-4. Histiastrum fasciatum, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 842.

Distance between the paired arms about half as large as their distance from the odd arm, which is somewhat larger. Each arm with six broad chambers, bisected by a radial septum; the terminal chamber convex, blunt, twice as broad as the basal chamber. Patagium incomplete, with concave chamber-rows, enveloping the arms with exception of the broad blunt terminal face.

Dimensions.—Radius of the paired arms 0.15, of the odd arm 0.16; basal breadth 0.05, terminal breadth 0.1 to 0.12.

Habitat.—Mediterranean (Messina), Atlantic (Canary Islands).

Subgenus 2. Pteractis, Ehrenberg, 1872 (loc. cit.).

Definition.—Arms provided with radial spines at the distal end.

10. Euchitonia elegans, Haeckel.

Pteractis elegans, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. viii. fig. 3.

Distance between the paired arms half as large as their distance from the odd arm. This latter is straight, while both the former are concavely curved towards the middle line. Arms five times as long as broad, at the distal end pointed and armed with a short conical terminal spine. Patagium nearly complete, enveloping four-fifths of the arms, with four to five concave chamber-rows.

Dimensions.—Radius of the arms 0.2, breadth of them 0.03.

Habitat.—Tropical Pacific, Philippine Sea, depth 3300 fathoms (Ehrenberg).

11. Euchitonia carcinus, n. sp. (Pl. 43, fig. 10).

Distance between the paired arms scarcely one-fourth as great as their distance from the odd arm. This latter is straight, twice as long as the former, which are concavely curved towards the middle line. The odd arm is three times as broad at the distal end as at the narrow base. The end of each arm is furnished with a strong triangular radial spine and a group of smaller spines. Patagium incomplete, with two to three concave chamber-rows, enveloping only the basal half of the arms.

Dimensions.—Radius of the paired arms 0.15, breadth 0.03; radius of the odd arm 0.3, breadth on its base 0.02, on its distal end 0.07.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

12. Euchitonia acuta, Stöhr.

Euchitonia acuta, Stöhr, 1880, Palæontogr., vol. xxvi. p. 111, Taf. v. fig. 6.

Distance between the paired arms two-thirds as great as their distance from the odd arm. All three arms nearly of the same size and form, two and a half times as long as broad, nearly lanceolate, at their broadest part one and a half times as broad as at their base. Patagium complete, enveloping the whole triangular disk, with five to six concave chamber-rows. In the figure of Stöhr the ends of the arms are simply pointed, while I find in the same fossil form a short terminal conical spine.

Dimensions.—Radius of all three arms 0.14; breadth at the base 0.04, at the broadest part 0.06.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Haeckel).

13. Euchitonia ypsiloides, Haeckel.

Histiastrum ypsiloides, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 843.

Distance between the paired arms two-thirds as great as their distance from the odd arm, which is somewhat larger. Length of the arms equals five times the breadth of the narrow base, which is half that of the distal end; this latter is armed with three to five short conical spines. Patagium complete, with six to seven concave chamber-rows, enveloping the whole arms with the exception of the terminal spines. (Differs from Euchitonia mülleri almost solely by the possession of terminal spines.)

Dimensions.—Radius of the arms 0.18 to 0.2; breadth at the base 0.04, at the distal end 0.08.

Habitat.—Mediterranean (Messina), Atlantic (Canary Islands), surface.

14. Euchitonia echinata, n. sp. (Pl. 43, fig. 11).

Distance between paired arms three-fourths as great as their distance from the odd arm, which is somewhat larger. Arms one and a half times as long as broad, somewhat constricted in the middle part, armed at the rounded ends with numerous (thirty to forty) strong, conical spines. Patagium complete, with four or five rectilinear parallel chamber-rows, enveloping the whole of the arms with the exception of the spiny ends.

Dimensions.—Radius of the arms (without spines) 0.2, breadth 0.06 to 0.09.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

Genus 231. Chitonastrum,^[57] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with three forked, chambered arms, without a patagium. (Arms and angles between them either equal or unequal.)

The genus Chitonastrum differs from its ancestral form, Dictyastrum, by the bifurcation of the distal ends of the arms. The few species of this genus are partly regular (like Dictyastrum), partly bilateral (like Rhopalastrum). If the number of species increases much, these two subgenera may be separated into two genera: Chitonastrella corresponding to the former, Chitonastromma to the latter.

Subgenus 1. Chitonastrella, Haeckel.

Definition.—All three arms of the same size and form, equidistant; fundamental form of the shell therefore an equilateral triangle.

1. Chitonastrum triglochin, n. sp.

All three arms equal and equidistant. Each arm has the form of an isosceles triangle, twice as high as broad; the truncated apex of the triangle is inserted into the large central disk, whilst its distal base (four times as broad) is divided by a deep incision (half as long as the arm). Each arm with ten to twelve joints, simple in its basal half, double in its distal half. Axes of the six branches straight. (Resembles Trigonastrum regulare, Pl. 43, fig. 16, but differs in the absence of a patagium.)

Dimensions.—Radius of each arm 0.24, greatest breadth 0.11, basal breadth 0.03.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

2. Chitonastrum bathybium, n. sp.

All three arms equal and equidistant, in the basal two-thirds simple, rectilinear, three times as long as broad, in the distal third forked, both branches equal, straight, blunt, half as broad as the basal part.

Dimensions.—Radius of each arm 0.18, basal breadth 0.04, breadth of the branches 0.02.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

Subgenus 2. Chitonastromma, Haeckel.

Definition.—One odd arm different in size or form from the two other arms, which are paired; distance between them different; fundamental form of the shell therefore a bilateral, isosceles triangle.

3. Chitonastrum jugatum, n. sp. (Pl. 43, fig. 14).

Dictyastrum jugatum, Haeckel, 1881, Prodromus et Atlas (pl. xliii. fig. 14).

Arms very different; odd arm club-shaped, twice as long as broad, at the blunt distal end twice as broad as at the base; its axis is perpendicular to the common axis of both paired arms, which are only two-thirds as long, not so broad, and in the distal half divided into two branches; the anterior branch is straight, nearly horizontal, the posterior shorter and curved backwards.

Dimensions.—Radius of the odd arm 0.2, of the paired arms 0.15; distal breadth of the former 0.08, basal breadth 0.04; breadth of the paired arms 0.04.

Habitat.—South Atlantic, Station 325, surface.

4. Chitonastrum dicranoides, n. sp.

All three arms in the basal half simple, nearly square, in the distal half forked; branches straight, blunt. Odd arm twice as large as the paired arms; angle between the latter larger than the angles between them and the odd arm. (The form of the arms resembles Dicranastrum furcatum, Pl. 47, fig 2.)

Dimensions.—Radius of the odd arm 0.24, of the paired arms 0.12; basal breadth 0.06.

Habitat.—North Atlantic, Station 353, surface.

5. Chitonastrum lyra, n. sp. (Pl. 43, fig. 15).

Dictyastrum lyra, Haeckel, 1881, Prodromus et Atlas (pl. xliii. fig. 15).

All three arms forked and nearly of the same size, but different in form and position. The distance between the branches of the two paired arms is only one-fourth of the distance between them and the odd arm. Each arm in the basal two-thirds is simple, with eleven to twelve transverse septa, in the distal third forked, each branch with four to five transverse septa. The branches of each arm are curved convexly one to another, ending obtusely. The axis of the simple proximal part is straight in the odd arm, in the paired arms curved concavely towards the middle line. In the figured specimen, which I observed living in Portofino (in September 1880), the central chamber of the central disk and the first surrounding ring were filled with the nucleus of the cell; both external rings were filled (like all chambers of the arms) with pink oil-globules of the red central capsule. From the mantle, enveloping the shell, radiated innumerable fine pseudopodia (much too short in the figure), and between the two paired arms a long "sarcode-flagellum."

Dimensions.—Radius of each arm 0.16; greatest breadth of the odd arm 0.04; basal breadth of the paired arms 0.02; distance of both branches of each arm 0.08.

Habitat.—Mediterranean, Portofino, near Genoa, Haeckel.

Genus 232. Trigonastrum,^[58] n. gen.

Definition.—Porodiscida with three forked, chambered arms, connected by a patagium. (Arms and angles between them either equal or unequal.)

The genus Trigonastrum differs from the preceding Chitonastrum, its ancestral form, in the development of a patagium between the arms. It bears therefore to the latter the same relation that Euchitonia does to Rhopalastrum.

Subgenus 1. Trigonastrella, Haeckel.

Definition.—All three arms of the same size and form, equidistant; fundamental form of the shell therefore a regular, equilateral triangle.

1. Trigonastrum regulare, n. sp. (Pl. 43, fig. 16).

Chitonastrum regulare, Haeckel, 1881, Prodromus et Atlas (pl. xliii. fig. 16).

All three arms equal and equidistant. Each arm has the form of an isosceles triangle, twice as high as broad, the truncated apex of which is inserted into the large circular central disk, whilst its distal base (four times as broad) is divided by a deep incision (half as long as the arm). Each arm with ten to twelve joints. Patagium between the arms nearly complete, spongy. (Differs from Chitonastrum triglochin mainly in the possession of a patagium.)

Dimensions.—Radius of each arm 0.24, greatest breadth 0.11, basal breadth 0.03; length of the sides of the regular triangle 0.45.

Habitat.—Pacific, central area, Station 274, surface.

Subgenus 2. Trigonastromma, Haeckel.

Definition.—One odd arm different in form or size from the other two arms, which are paired; distance between them different; fundamental form of the shell therefore an isosceles triangle.

2. Trigonastrum krohnii, Haeckel.

Euchitonia krohnii, Haeckel, 1862, Monogr. d. Radiol., p. 507.

All three arms different; distance between the two paired arms smaller than their distance from the odd arm. Odd arm with six joints. Each paired arm with seven joints, increasing in breadth towards the distal end. Odd arm and one paired arm forked at the end, the other paired arm simple. Patagium nearly complete. (The asymmetry in this form may perhaps be an individual anomaly, as also in Myelastrum anomalum, Pl. 47, fig. 9.)

Dimensions.—Radius of the arms about 0.13 to 0.16, breadth 0.05 to 0.08.

Habitat.—North Atlantic, Funchal, Madeira, Krohn, surface.

3. Trigonastrum gegenbauri, Haeckel.

Euchitonia gegenbauri, Haeckel, 1862, Monogr. d. Radiol., p. 506, Taf. xxxi. figs. 2, 3.

Arms different; distance between the paired arms larger than their distance from the odd arm, which is one-third shorter. Odd arm egg-shaped, simple, with seven joints, undivided. Both paired arms equal, with ten joints, in the distal third forked. Patagium nearly complete.

Dimensions.—Radius of the odd arm 0.14, greatest breadth 0.08; radius of the paired arms 0.2.

Habitat.—Mediterranean (Messina), Haeckel, surface.

Genus 233. Stauralastrum,^[59] n. gen.

Definition.—Porodiscida with four simple, undivided, chambered arms, without a patagium; quadrangular shell a regular cross, with four equal arms placed at right angles.

The genus Stauralastrum is the most simple form of the Tessarastrida, or of those Porodiscida in which the margin of the central disk is armed with four chambered arms. In Stauralastrum these four arms are quite simple and equal, without a patagium, separated by four right angles, so that the whole shell represents a regular rectangular cross. If we connect the distal points of the arms by lines, we get a complete square. (In my Prodromus, 1881, the species of this genus were united with Hagiastrum, which genus I now retain for the simple bilateral Tessarastrida.)

Subgenus 1. Stauralastrella, Haeckel.

Definition.—Ends of the arms blunt, without terminal spines.

1. Stauralastrum cruciforme, n. sp. (Pl. 45, fig. 6).

Arms very thin, nearly linear, four to five times as long as broad, of equal breadth at the base and at the truncated distal end; their breadth equals one-third of the radius of the central disk. Edges of the arms parallel.

Dimensions.—Radius of each arm 0.8, breadth 0.016.

Habitat.—South Pacific, Station 293, surface.

2. Stauralastrum lanceolatum, n. sp.

Arms lanceolate, three times as long as broad, in their middle part three times as broad as at both ends; their greatest breadth nearly equals the diameter of the central disk. (The arms have the same form as in Euchitonia lanceolata, Pl. 43, fig. 9.) Edges of the arms convex.

Dimensions.—Radius of each arm 0.3, greatest breadth (in the middle part) 0.08.

Habitat.—Pacific, central area, Station 273, depth 2350 fathoms.

3. Stauralastrum ordo, n. sp.

Arms trapezoid, about as long as broad, twice as broad at their truncated distal end as at the base; their basal breadth equals the radius of the central disk, which exhibits two to three rings. (The arms have nearly the same form as those in Hagiastrum mosis, Pl. 45, fig. 3.) Edges of the arms rectilinear, divergent towards the ends.

Dimensions.—Radius of each arm 0.12, basal breadth 0.04, distal breadth 0.08.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

4. Stauralastrum clavigerum, n. sp.

Arms twice as long as broad, in their distal half lenticular, nearly circular, twice as broad as in their square proximal half; their distal breadth equals the diameter of the central disk, which exhibits three to four rings. Edges of the arms concave.

Dimensions.—Radius of each arm 0.2, basal breadth 0.04, distal breadth 0.08.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

5. Stauralastrum dilatatum, n. sp.

Arms of nearly equal length and breadth, at their convex distal end three times as broad as at their narrow base; their distal breadth three times as large as the radius of the central disk, which exhibits three to four rings. (Resembles Histiastrum quadrigatum, Pl. 46, fig. 3, but has no patagium.) Edges of the arms concave.

Dimensions.—Radius of each arm 0.15, basal breadth 0.04, terminal breadth 0.12.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

Subgenus 2. Stauralastromma, Haeckel.

Definition.—Ends of the arms with one or more terminal spines.

6. Stauralastrum rhopalophorum, n. sp. (Pl. 45, fig. 1).

Hagiastrum rhopalophorum, Haeckel, 1881, Prodromus, p. 460.

Arms cylindrical, eight times as long as broad at their base, at their distal end club-shaped, three times as broad as at their base; their distal breadth twice as large as the diameter of the central disk, which exhibits two to three rings. Surface thorny, with larger spines towards the end, and one radial, very strong, angular terminal spine. Edges of the arms parallel.

Dimensions.—Radius of each arm (without terminal spine) 0.32, basal breadth 0.03, terminal breadth 0.1.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

7. Stauralastrum antiquum, n. sp.

Rhopalastrum sp. Bury, 1862, Polycystins of Barbados, pl. xiv. fig. 5.

Arms six times as long as broad at their base, in their distal half nearly spherical, three times as broad as in their cylindrical basal half; their distal breadth nearly equals the diameter of the central disk which exhibits three to four rings. On the end of each arm one strong, angular, terminal spine. (Differs from the preceding species by larger central disk and stouter arms, also by less developed spines.) Edges of the arms parallel.

Dimensions.—Radius of each arm 0.25, basal breadth 0.04, terminal breadth 0.12.

Habitat.—Fossil in the Barbados rocks; and living in the depths of the Central Pacific, Station 266, depth 2750 fathoms.

8. Stauralastrum staurolonche, n. sp.

Arms four times as long as broad at their base, gradually increasing towards their truncated end, which is one and a half times as broad as their base; their distal breadth equals the radius of the central disk, which exhibits four to five rings. At the end of each arm is a very strong conical terminal spine. (Resembles Histiastrum quaternarium, Abhandl. k. Akad. Wiss. Berlin, 1875, Taf. xxiv. fig. 3, but has no patagium.) Edges of the arms rectilinear, divergent.

Dimensions.—Radius of each arm 0.25, basal breadth 0.045, distal breadth 0.07.

Habitat.—Fossil in the Barbados rocks; and living in the depth of the Equatorial Atlantic, Station 348, depth (2450) fathoms.

9. Stauralastrum horridum, n. sp.

Arms three times as long as broad at their base, gradually increasing towards their rounded end, which is twice as broad as their base, their distal breadth equals the diameter of the central disk, which exhibits four to five rings. Surface thorny, at the distal end of each arm is a group of twenty to twenty-five smaller and five to six larger, straight, conical spines. Edges of the arms rectilinear, divergent.

Dimensions.—Radius of each arm 0.15, basal breadth 0.05, distal breadth 0.1.

Habitat.—Pacific, central area, Station 270, depth 2925 fathoms.

Genus 234. Hagiastrum,^[60] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with four simple, undivided, chambered arms, without a patagium; quadrangular shell bilateral, two opposite arms of the main axis (or principal arms) different from the two others (or lateral arms).

The genus Hagiastrum, as here defined, was formerly united by me with the foregoing Stauralastrum, but differs from it by the bilateral or symmetrical form. Whilst in the latter all four arms and the four angles between them are equal, they are here differentiated into pairs.

Subgenus 1. Hagiastrella, Haeckel.

Definition.—Both longitudinal arms of equal size and form.

1. Hagiastrum buddhae, n. sp. (Pl. 45, fig. 5).

Cross rectangular. Both longitudinal arms of equal size, twice as long as the transverse arms; all arms smooth, club-shaped, twice as broad at their globose distal part as at their base, each with three large conical terminal spines.

Dimensions.—Radius of the principal arms 0.4, of the lateral arms 0.2; basal breadth 0.06, distal breadth 0.12.

Habitat.—Indian Ocean, Belligemma, Ceylon, surface, Haeckel.

2. Hagiastrum bramae, n. sp.

Cross rectangular. Both longitudinal arms of equal size, one and a half times as long as the transverse arms; all arms thorny, club-shaped, at their pear-shaped distal part three times as broad as at their base, provided with numerous conical spines, one larger terminal spine at their distal point. (Resembles Stauralastrum rhopalophorum, Pl. 45, fig. 1, but is distinguished by the different size of the arm-pairs, and by the stronger spines.)

Dimensions.—Radius of the principal arms 0.3, of the lateral arms 0.2; basal breadth 0.04, distal breadth 0.12.

Habitat.—Indian Ocean, off Maldive Islands, surface, Haeckel.

Subgenus 2. Hagiastromma, Haeckel.

Definition.—The two longitudinal arms different in size or form.

3. Hagiastrum mosis, n. sp. (Pl. 45, fig. 3).

Cross rectangular. All four arms nearly isosceles, triangular, at their narrow base half as broad as at their truncated, concavely fluted, distal end. The posterior principal arm with twelve to thirteen joints, twice as long as the anterior arm, which has six to seven joints and is one and a half times as long as the two lateral arms (with four to five joints).

Dimensions.—Radius of the posterior arm 0.3, of the anterior 0.15, of the lateral arms 0.1; basal breadth 0.05, terminal breadth 0.1.

Habitat.—Mediterranean (Smyrna), surface, Haeckel.

4. Hagiastrum mohammedis, n. sp.

Cross with unequal angles, the anterior little smaller than the posterior. All four arms club-shaped, thorny, three times as broad at their globose distal end as at their narrow base, and furnished with ten to twelve conical spines. Posterior principal arm twice as long as the anterior, and four times as long as the rudimentary lateral arms.

Dimensions.—Radius of the posterior arm 0.4, of the anterior 0.2, of the lateral arms 0.1; basal breadth 0.02 to 0.03, distal breadth 0.06 to 0.1.

Habitat.—Philippine Sea, Samboangan, Station 200, surface.

5. Hagiastrum christi, n. sp.

Cross with unequal angles, the anterior somewhat smaller than the posterior. All four arms of similar form, lanceolate, in their middle twice as broad as at either obtuse end. The posterior principal arm with twelve joints, one and a half times as long as the anterior (with nine joints) and twice as long as the two lateral arms (each with six joints). The form and structure of the arms in this species are nearly the same as in Tessarastrum straussi (Pl. 45, fig. 8); but the arms are broader in the middle, and are not connected by a patagium.

Dimensions.—Radius of the principal posterior arm 0.2, of the anterior 0.15, of each lateral arm 0.1; greatest breadth (in the width) 0.01, basal breadth 0.03.

Habitat.—North Atlantic, Færöe Channel, Gulf Stream, surface, John Murray.

Genus 235. Histiastrum,^[61] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Porodiscida with four simple, undivided, chambered arms, connected by a patagium; square shell a regular cross, with four equal arms and four right angles between them.

The genus Histiastrum, quite insufficiently characterised by Ehrenberg (1847), was afterwards (1875) illustrated by the figures of two different fossil species. One of these, Histiastrum ternarium, with three arms, belongs to Hymeniastrum; the other, Histiastrum quaternarium, is here retained as the true, typical representative species of the genus. It differs from its ancestral form Stauralastrum, by the possession of a patagium, from Tessarastrum by the regular square form of the shell.

Subgenus 1. Histiastrella, Haeckel.

Definition.—Distal ends of the arms blunt, without terminal spines.

1. Histiastrum quadrigatum, n. sp. (Pl. 46, fig. 3).

Arms at their distal end nearly as broad as long, and four times as broad as at their narrow base; their lateral edges concave, their terminal edge convex, without spines. Each arm is divided by seven to eight convex transverse septa into eight to nine simple, broad chambers. Central disk with three to four rings, about as broad as the fifth chamber. Patagium complete, connecting all the lateral edges of the arms.

Dimensions.—Radius of each arm 0.15, basal breadth 0.03, terminal breadth 0.12.

Habitat.—Equatorial Atlantic, Station 347, surface.

2. Histiastrum excisum, n. sp.

Arms four times as long as broad at their base, and twice as broad at their rounded blunt distal end as at their base; their lateral edges rectilinear, divergent. Central disk with three to four rings, somewhat broader than their distal end. Patagium incomplete, connecting only the basal half of the arms, with three to four concave chamber-rows, on the margin concave. (May be regarded as Euchitonia mülleri, with four arms.)

Dimensions.—Radius of each arm 0.2, basal breadth 0.05, distal breadth 0.1.

Habitat.—Atlantic, surface, Canary Islands.

3. Histiastrum velatum, n. sp. (Pl. 46, fig. 4).

Dictyastrum velatum, Haeckel, 1879, Atlas (pl. xlvi. fig. 4).

Arms pear-shaped, rapidly increasing from their narrow base, nearly circular, little longer than broad; each with eight to nine transverse chamber-rows; their lateral edges at their base concave, at their end circular. Central disk with three to four rings, somewhat smaller than one arm. Patagium complete, with six to seven radial beams, filling out perfectly the intervals between the arms. A peculiar girdle of finer network and equal breadth surrounds the whole equatorial periphery of the disk, and gives it the appearance of a square with rounded corners.

Dimensions.—Radius of each arm 0.2, basal breadth 0.03, distal breadth 0.12.

Habitat.—South Atlantic, Station 330, surface.

Subgenus 2. Histiastromma, Haeckel.

Definition.—Distal ends of the arms spiny, furnished with one or more terminal spines.

4. Histiastrum quaternarium, Ehrenberg.

Histiastrum quaternarium, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxiv. figs. 3, 4.

Arms six times as long as broad at their base, with rectilinear, little divergent edges; at their truncated distal end a little broader, with one single, very strong, conical, terminal spine. Central disk with four to five rings, somewhat broader than the arm. Patagium incomplete, enveloping only the basal half of the arms.

Dimensions.—Radius of each arm 0.18, basal breadth 0.03, distal breadth 0.05.

Habitat.—Fossil in the rocks of Barbados.

5. Histiastrum gladiatum, n. sp.

Astromma sp., Bury, 1862, Polycystins of Barbados, pl. v. fig. 1.

Arms triangular, eight times as long as broad at their base; at their distal end three times as broad as at their base, with rectilinear, divergent edges; their truncated end with a large conical, terminal spine. Central disk with four to five rings, broader than the arms. Patagium incomplete, enveloping only the basal half of the arms.

Dimensions.—Radius of each arm 0.12, basal breadth 0.013, distal breadth 0.04.

Habitat.—Fossil in the rocks of Barbados; and living in the depth of the Central Pacific, Station 268, depth 2900 fathoms.

6. Histiastrum boseanum, n. sp. (Pl. 46, fig. 1).

Arms linear, twelve times as long as broad at their base (at their distal end twice as broad as at their base), with rectilinear, parallel edges. The club-shaped end thickened, dentate, with two lateral rows of strong teeth in the equatorial plane, and with one very stout, angular, terminal spine. Central disk with two to three rings, broader than the arms. Patagium incomplete, with four to five concave chamber-rows, enveloping only the basal half of the arms. I call this splendid species in honour of Dr. Graf Bose, the great friend of nature and patron of the University of Jena.

Dimensions.—Radius of each arm 0.25, basal breadth 0.02, distal breadth 0.05.

Habitat.—Indian Ocean, Madagascar, Rabbe.

7. Histiastrum coronatum, n. sp.

Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pl. iv. fig. 1.

Arms linear, eight times as long as broad, with rectilinear parallel edges; the thickened, nearly spherical, distal end three times as broad, with five strong conical spines, one middle (perradial) larger and two smaller on each side of it. Central disk with two to three rings, of the same breadth as the terminal knot of the arms. Patagium incomplete, square, enveloping the arms, with the exception of the knot.

Dimensions.—Radius of each arm 0.16, basal breadth 0.02, terminal breadth 0.06.

Habitat.—Fossil in the rocks of Barbados.

8. Histiastrum circulare, n. sp.

Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pl. xxiii. fig. 1.

Arms linear in their inner half, egg-shaped and three times as broad in their outer half, with ten to twelve strong terminal spines, the middle (perradial) larger, in all three times as long as broad. Central disk with three to four rings, broader than their distal knobs. Patagium nearly complete, circular, enveloping the whole arms, with exception of the outermost end.

Dimensions.—Radius of each arm 0.22, basal breadth 0.02, terminal breadth 0.06.

Habitat.—Fossil in the rocks of Barbados; and living in the depths of the Central Pacific, Station 268, depth 2900 fathoms.

9. Histiastrum pentadiscus, n. sp. (Pl. 46, fig. 2).

Arms in their inner half linear, twice as long as broad, in their outer half circular, three times as broad, with the same structure as the central disk, exhibiting three concentric rings around one central chamber. Patagium complete, spongy, with radiating beams, enveloping the whole disk, with the exception of the outermost end of the arms, which is armed with twelve to sixteen strong conical spines, the middle (perradial) spine much larger.

Dimensions.—Radius of each arm (without terminal spine) 0.18, basal breadth 0.025, terminal breadth 0.08.

Habitat.—South Atlantic, Station 333, surface.

Genus 236. Tessarastrum,^[62] n. gen.

Definition.—Porodiscida with four simple, undivided, chambered arms, connected by a patagium; quadrangular shell bilateral, two opposite arms of the main axis (or principal arms) different from the two others (or lateral arms).

The genus Tessarastrum, formerly united by me with Histiastrum, differs from the latter in its bilateral or symmetrical form, and bears therefore the same relation to it that Hagiastrum does to Stauralastrum.

Subgenus 1. Tessarastrella, Haeckel.

Definition.—Both longitudinal arms of equal size and form.

1. Tessarastrum straussii, n. sp. (Pl. 45, fig. 8).

Histiastrum straussii, Haeckel, 1881, Prodromus et Atlas (pl. xlv. fig. 8).

Cross not rectangular. Both principal arms of equal size and form, four times as long as broad, and twice as long as the broader lateral arms; the former with ten to eleven, the latter with five to six joints, separated by convex transverse septa. Distal ends of the arms blunt. Axes of the smaller arms not perpendicular to that of the larger arms; therefore the anterior angles between them smaller than the posterior angles. Patagium between the arms incomplete. I call this remarkable species after the great German philosopher David Strauss.

Dimensions.—Radius of the principal arms 0.24, of the lateral arms 0.12; greatest breadth (in the middle) of the former 0.05, of the latter 0.06.

Habitat.—North Pacific, Hyalonema-ground, March 5, 1875.

2. Tessarastrum spinozæ, n. sp.

Cross rectangular. Both principal arms of equal size and form, ten times as long as broad, and twice as long as the lateral arms, which are only five times as long as broad. All arms linear, at their distal end club-shaped, and armed with twenty to thirty very strong angular spines. Patagium incomplete, enveloping only the basal half of the arms. (Resembles Histiastrum boseanum, Pl. 46, fig. 1, but differs in the broader arms and the unequal size of both pairs.) I call this species after the great monistic philosopher Benedictus Spinoza.

Dimensions.—Radius of the principal arms 0.3, of the lateral arms 0.16; basal breadth 0.025, distal breadth 0.05.

Habitat.—South Atlantic, Station 333, surface.

3. Tessarastrum brunonis, n. sp. (Pl. 45, fig. 9).

Histiastrum brunonis, Haeckel, 1881, Prodromus et Atlas (pl. xlv. fig. 9).

Cross rectangular. Both principal arms of equal size and form, three times as long as broad, each with ten joints, three times as long as the lateral arms, which are nearly square, with four joints. All arms rounded, at their truncated end little broader than at their base. No spines. Patagium complete, envelops the whole shell, and is composed of two parallel lattice-lamellæ on each side of the flat disk, which are connected by very fine perpendicular bars. This is shown clearly in fig. 9, Pl. 45, where the disk is seen from the edge. I call this species after the great Italian philosopher Giordano Bruno.

Dimensions.—Radius of the principal arms 0.22, of the lateral arms 0.12; basal breadth 0.04, distal breadth 0.05.

Habitat.—South Pacific, Station 285, depth 2375 fathoms.

Subgenus 2. Tessarastromma, Haeckel.

Definition.—The two principal arms of different size or form.

4. Tessarastrum democriti, n. sp. (Pl. 45, fig. 7).

Histiastrum democriti, Haeckel, 1881, Prodromus et Atlas (pl. xlv. fig. 7).

Cross not rectangular; the two anterior angles smaller than the two posterior. All four arms club-shaped, twice as broad at their rounded obtuse distal end as at their base, of unequal length. Posterior principal arm one and a fourth times as long as the posterior, and one and two-thirds as long as the lateral arms. Patagium incomplete, enveloping only the basal half of the arms. I call this species after the great Greek philosopher Democritus.

Dimensions.—Radius of the posterior arm 0.3, of the anterior 0.25, of each lateral arm 0.22; basal breadth 0.05, distal breadth 0.1.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Genus 237. Stephanastrum,^[63] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Porodiscida with four simple, undivided, chambered arms, connected on the distal ends by a spongy, square or rhomboidal, patagial girdle (or a patagium with four large, interbrachial openings). Shell either regular or bilateral (with equal or unequal arms).

The genus Stephanastrum, founded (1847) by Ehrenberg for the very peculiar Stephanastrum rhombus, differs from the nearly allied foregoing genera in the imperfect development of the peculiar patagium, connecting only the distal ends of the four arms, while it is absent at their base. Two new species, different from Stephanastrum rhombus by the regular square form, were found in the Challenger collection.

Subgenus 1. Stephanastrella, Haeckel.

Definition.—All four arms of the cross have the same size.

1. Stephanastrum quadratum, n. sp. (Pl. 46, fig. 5).

All four arms of the same size, six times as long as broad at their base, ending with a strong, short, four-sided pyramidal spine. In the outer half of each arm are two opposite lateral spongy wings, which form an equilateral triangle, and from union of the bases of the four triangles arises the peculiar patagium, which forms a square with four large interbrachial openings.

Dimensions.—Radius of each arm 0.25, basal breadth 0.035; length of the sides of the square patagium 0.3.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

2. Stephanastrum capitatum, n. sp. (Pl. 44, fig. 1).

All four arms of the same size, five times as long as broad at their base, at their distal end with a spongy, nearly spherical capitulum of twice their breadth, provided with a very strong, angular, pyramidal, terminal spine (half as long as the arm). All four arms connected by a square patagium, arising immediately below the capitula, and perforated by four large interbrachial openings.

Dimensions.—Radius of each arm (without the terminal spine) 0.25, basal breadth 0.05; length of the sides of the square patagium 0.3.

Habitat.—Pacific, central area. Station 265, depth 2900 fathoms.

Subgenus 2. Stephanastromma, Haeckel.

Definition.—Two opposite arms of the cross larger than the two others.

3. Stephanastrum rhombus, Ehrenberg.

Stephanastrum rhombus, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 33; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxv. fig. 1.

Two arms of the longitudinal axis one and a third times as long as two arms of the transverse axis. All four arms linear, about eight times as long as broad, at their distal end somewhat thickened, club-shaped, with a pyramidal terminal spine. The ends of the arms are connected by a riband-shaped, straight, spongy patagium of the same breadth as the arms. Between the rhomboidal patagium and the arms remain four large rectangular triangles as interbrachial openings.

Dimensions.—Radius of the longer arms 0.2, of the shorter 0.15; basal breadth 0.02; length of the sides of the rhombic patagium 0.25.

Habitat.—Fossil in the rocks of Barbados.

Genus 238. Dicranastrum,^[64] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with four forked, spongy, or chambered arms, without a patagium; shell regular (not bilateral), with four equal arms crossed at right angles.

The genus Dicranastrum comprises a number of very remarkable, hitherto unknown, Euchitonida, which are rather common in the Pacific (mainly on the surface), and characterised by the bifurcation of the cross-arms of the regular square shell. It bears therefore to its probable ancestral form, Stauralastrum, the same relation that in the triradiate Euchitonida Chitonastrum does to Dictyastrum. The arms are commonly of very delicate structure, more or less spongy.

Subgenus 1. Dicranaster, Haeckel.

Definition.—Each cross-arm with two simple branches.

1. Dicranastrum furcatum, n. sp. (Pl. 47, fig. 2).

Arms simply forked, three times as long as broad at their base, with eight blunt ends of the fork-branches. The simple proximal half of each arm about the same size as each branch of the dichotomous distal part, twice as long as broad. Edges of the arms ragged.

Dimensions.—Radius of each arm 0.38, basal breadth 0.12; breadth of the forked part 0.3.

Habitat.—Pacific, central area, Station 271, surface.

2. Dicranastrum dichotomum, n. sp.

Arms simply forked, four times as long as broad at their base; each arm with two blunt branches. The simple proximal part of each arm is three times as long and twice as broad as each branch of the dichotomous distal part. Ends of the arms blunt, truncated.

Dimensions.—Radius of each arm 0.35, basal breadth 0.08; breadth of the forked part 0.2.

Habitat.—South Pacific, Station 281, surface.

3. Dicranastrum cornutum, n. sp. (Pl. 45, fig. 2).

Hagiastrum cornutum, Haeckel, 1879, Atlas (pl. xlv. fig. 2).

Four arms simply forked, four times as long as broad; each arm with two triangular diverging branches ending in strong conical spines. The simple basal part of each arm about of the same length as each branch of the distal part, twice as long as broad. Distance between the terminal spines of each arm nearly as great as its length.

Dimensions.—Radius of the arm 0.24, basal breadth 0.05; breadth across the bifurcation 0.12.

Habitat.—South Atlantic, Station 325, surface.

4. Dicranastrum antilope, n. sp.

Four arms simply forked, three times as long as broad; each arm with two lanceolate diverging branches, ending in strong angular spines. The simple basal part of each arm is twice as long as each branch of the distal part. Distance of the two terminal spines of each arm scarcely half as great as its length.

Dimensions.—Radius of the arm 0.32, basal breadth 0.11; breadth of the branches 0.07.

Habitat.—Tropical Atlantic (off Ascension), Station 342, surface.

Subgenus 2. Tricranastrum, Haeckel, 1881, Prodromus, p. 460.

Definition.—Each cross arm with three terminal branches, one middle (perradial) and two lateral (adradial) branches.

5. Dicranastrum wyvillei, n. sp. (Pl. 47, fig. 3).

Tricranastrum wyvillei, Haeckel, 1879, Natürl. Schöpfungsgesch., p. 705, Taf. xvi. fig. 5.

Arms trifid, one and a half times as long as broad; each arm with three blunt terminal branches of equal size. The simple basal part of each arm twice as long as the trifid distal part. (The central capsule depicted in fig. 3, Pl. 47, has the same form as the skeleton, and is only a little smaller.)

Dimensions.—Radius of the arm 0.4, basal breadth 0.12, greatest breadth (in the distal part) 0.24.

Habitat.—Pacific, central area, Station 271, surface.

6. Dicranastrum tricuspis, n. sp.

Arms trifid, twice as long as broad; each arm with three pointed terminal branches, ending in strong conical spines, the middle branch somewhat larger than the other two. The simple basal part of each arm three times as long as the trifid distal part.

Dimensions.—Radius of the arm 0.3, basal breadth 0.06, greatest breadth (in their distal part) 0.15.

Habitat.—North Pacific, Station 244, surface.

7. Dicranastrum trifarium, n. sp.

Arms trifid, three times as long as broad at their base; each arm with three pointed terminal branches, ending in strong sulcate spines; the middle branch twice as large as the two others. The simple basal part of each arm two and a half times as long as the trifid distal part.

Dimensions.—Radius of the arm 0.35, basal breadth 0.03, greatest breadth (in the distal part) 0.05.

Habitat.—South Pacific, Station 298, surface.

Subgenus 3. Tetracranastrum, Haeckel.

Definition.—Each cross-arm with four terminal branches, the two fork-branches being again bifurcated.

8. Dicranastrum bifurcatum, n. sp. (Pl. 47, figs. 1, 1a).

Arms doubly forked or quadripartite, six times as long as broad at their base; each arm in its proximal half simple, three times as long as broad; in its distal half doubly forked; the secondary branches with blunt, roundish ends, nearly as large as the primary branches. Central disk (fig. 1a) with three concentric rings around the central chamber; from its periphery radiate thin radial beams in the spongy framework of the delicate arms. The central capsule has the same form as the skeleton, and is only a little smaller.

Dimensions.—Radius of the arm 0.45, basal breadth 0.08; breadth of the terminal branches 0.03.

Habitat.—North Pacific, east of Japan, Station 241, surface.

Genus 239. Myelastrum,^[65] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with four forked, spongy, or chambered arms, without a patagium; shell bilateral, with paired different arms; two equal anterior arms of different shape from the two equal posterior arms.

The genus Myelastrum differs from the foregoing Dicranastrum, the ancestral form, by the twofold differentiation of the four arms. Whilst in the latter all four arms are equal, separated by equal angles, here the two anterior arms are constantly different from the two posterior. The lateral angles between the two arm-pairs are equal, while the posterior and the anterior angle (between the two arms of each pair) are more or less different. The shell assumes, therefore, a very characteristic bilateral form, similar to the "quadricorn cross" of the grey central substance in the transverse section of the human medulla spinalis. Though the spongy shell is commonly a most delicate and thin disk it nevertheless reaches unusual dimensions, its diameter in some species being more than a millimetre.

Subgenus 1. Myelastrella, Haeckel.

Definition.—Posterior arms simple, undivided; anterior arms lobated or cleft, with one or more incisions at the distal end.

1. Myelastrum medullare, n. sp. (Pl. 47, fig. 13).

Anterior arms bifid, nearly square, with a shallow incision at their broad truncated end. Posterior arms somewhat smaller, nearly triangular, with simple blunt ends. Sagittal constriction three-fourths as large as the transverse one. Surface smooth.

Dimensions.—Radius of the anterior arms 0.36, of the posterior 0.3; longitudinal constriction 0.24, transverse 0.36.

Habitat.—Pacific, central area, Station 271, surface.

2. Myelastrum spinale, n. sp.

Anterior arms bifid, twice as long as broad, with a deep incision at their truncated end. Posterior arms slender, half as large, with simple blunt ends. Sagittal constriction one and a half times as large as the transverse. Surface spiny.

Dimensions.—Radius of the anterior arms 0.4, of the posterior 0.2; longitudinal constriction 0.3, transverse 0.2.

Habitat.—North Pacific, Station 248, surface.

3. Myelastrum heteropterum, n. sp. (Pl. 47, fig. 8).

Anterior arms trifid, about as long as broad, with two incisions at their broad truncated end. Posterior arms about half as large, simple, with rounded blunt ends. Sagittal constriction two-thirds as large as the transverse. Surface bristly.

Dimensions.—Radius of the anterior arms 0.65, of the posterior 0.035; longitudinal constriction 0.4, transverse 0.6.

Habitat.—South Pacific, Station 291, surface.

Subgenus 2. Myelastromma, Haeckel.

Definition.—All four arms (posterior as well as anterior) lobated or cleft.

4. Myelastrum octocorne, n. sp. (Pl. 47, fig. 12).

All four arms with a deep incision in their distal half; anterior arms broader, but shorter than the posterior; in the anterior arms the two lobes are of the same size, in the posterior arms the median lobe is longer than the lateral lobe. Sagittal constriction little smaller than the transverse. Surface of the disk rough.

Dimensions.—Radius of the anterior arms 0.45, of the posterior 0.62; longitudinal constriction 0.25, transverse 0.3.

Habitat.—Pacific, central area, Station 271, surface.

5. Myelastrum farfalla, n. sp. (Pl. 47, fig. 10).

All four arms with a shallow incision at their distal end. Anterior arms broader, but shorter than the posterior; in each arm the anterior lobe is shorter than the posterior. Sagittal constriction smaller than the transverse. Surface smooth.

Dimensions.—Radius of the anterior arms 0.4, of the posterior 0.6; longitudinal constriction 0.5, transversal stricture 0.6.

Habitat.—Pacific, central area, Station 274, surface.

6. Myelastrum papilio, n. sp. (Pl. 47, fig. 6).

All four arms with a shallow incision at their distal end. Anterior arms triangular, of the same breadth, but of the double length of the square posterior arms. Sagittal and transverse constrictions of the same length. Surface ciliated. (Resembles a butterfly.)

Dimensions.—Radius of the anterior arms 0.7, of the posterior 0.4; longitudinal and transverse constrictions 0.4.

Habitat.—North Pacific, near Japan, Station 241, surface.

7. Myelastrum decaceros, n. sp. (Pl. 47, fig. 7).

Anterior arms bifid, with one shallow incision at their distal end. Posterior arms of the same length, but much broader, trifid, with two incisions (one larger and one smaller). Sagittal and transverse constrictions of the same length. Surface spiny.

Dimensions.—Radius of all four arms 0.4; longitudinal and transverse constrictions 0.35.

Habitat.—Pacific, central area, Station 272, surface.

8. Myelastrum dodecaceros, n. sp. (Pl. 47, figs. 11, 11a).

Anterior arms trifid, with two shallow incisions at their distal end. Posterior arms about one-third larger, also trifid, with one deeper anterior and one shallower posterior incision. Sagittal constriction much longer than the transverse. Surface ciliated, covered with numerous thin and long radial bristles (fig. 11a).

Dimensions.—Radius of the anterior arms 0.5, of the posterior 0.7; longitudinal constriction 0.5, transverse 0.35.

Habitat.—Pacific, central area, Station 270, surface.

9. Myelastrum ciliatum, n. sp.

Anterior arms trifid, with two shallow incisions. Posterior arms somewhat smaller, also trifid, with two deeper incisions. Sagittal constriction a little larger than the transverse. Margin of the disk ciliated, with radial bristle-shaped spines, as prolongations of the inner radial beams, arising from the central disk.

Dimensions.—Radius of the anterior arms 0.6, of the posterior 0.5; longitudinal constriction 0.4, transverse 0.35.

Habitat.—South Pacific, Station 288, surface.

10. Myelastrum lobatum, n. sp.

Anterior arms somewhat broader but shorter than the posterior arms. Each arm four-lobed, with three terminal shallow incisions of nearly equal size. Sagittal constriction smaller than the transverse. Surface of the disk bristly.

Dimensions.—Radius of the anterior arms 0.4, of the posterior 0.5; longitudinal constriction 0.3, transverse 0.35.

Habitat.—North Pacific, Station 253, surface.

11. Myelastrum rotula, n. sp.

Anterior arms little broader than the posterior, but of the same length. Each arm four-lobed, with three terminal deep incisions of equal size. Sagittal and transverse constrictions equal. The whole disk nearly circular, resembles a wheel with sixteen spokes. Surface smooth.

Dimensions.—Radius of all four arms 0.5; longitudinal and transverse constrictions 0.3.

Habitat.—Pacific, central area, Station 274, surface.

12. Myelastrum giganteum, n. sp.

Anterior arms somewhat broader and shorter than the posterior. Each arm four-lobed, with three shallow terminal incisions, the middle incision twice as deep as the two laterals. Sagittal constriction a little larger than the transverse. Margin ciliated, with radial bristle-shaped spines as prolongations of the inner radial beams, proceeding from the central disk (as in Myelastrum dodecaceros, Pl. 47, figs. 11, 11a).

Dimensions.—Radius of the anterior arms 0.6, of the posterior 0.8; longitudinal constriction 0.6, transverse 0.5.

Habitat.—Pacific, central area, Station 271, surface.

13. Myelastrum anomalum, n. sp. (Pl. 47, fig. 9).

All four arms of different size and form; anterior arms broader, posterior longer; one anterior arm trifid, the three other arms bifid; length of the branches unequal; all four angles between the arms unequal. (This anomalous form, seen only once, may be an individual abnormality.)

Dimensions.—Radius of the arms 0.4 to 0.7; constrictions 0.3.

Habitat.—North Pacific, Station 237, surface.

Genus 240. Pentalastrum,^[66] Haeckel, 1881, Prodromus, p. 461.

Definition.—Porodiscida with five simple, undivided, chambered arms, without a patagium.

The genus Pentalastrum opens the small series of Euchitonida, in which the shell is not provided with three or four arms, as usual, but with five. All forms of this little group are rare. Some species resemble in their external form and in the articulation of their arms certain forms of Asterida. In Pentalastrum, the most simple genus, the five arms are simple, not forked, and without a patagium. It can be derived from Dictyastrum or Stauralastrum by increase of the number of arms.

Subgenus 1. Pentalastrella, Haeckel.

Definition.—All five arms equal, with equal angles between them. Shell a regular pentagon.

1. Pentalastrum asteracanthion, n. sp.

All five arms equal, club-shaped, at their thickened obtuse end three times as broad as at their base, twice as long as broad. Angles between the arms equal.

Dimensions.—Radius of each arm 0.2, basal breadth 0.03, distal breadth 0.08.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

2. Pentalastrum astropecten, n. sp.

All five arms equal, with five to six distinct, simple joints, the basal joint two-thirds as broad as the terminal joint, which bears a strong conical spine. Angles between the arms equal. (Resembles Pentinastrum asteriscus, Pl. 44, fig. 2, but has no patagium.)

Dimensions.—Radius of each arm 0.14, basal breadth 0.024, distal breadth 0.036.

Habitat.—Pacific, central area, Station 263, depth 2650 fathoms.

Subgenus 2. Pentalastromma, Haeckel.

Definition.—Arms of different sizes, one odd arm larger than the two others; the opposite odd angle generally different from the four other angles.

3. Pentalastrum ophidiaster, n. sp. (Pl. 44, fig. 3).

Arms nearly triangular, at their obtuse truncated distal end twice as broad as at their base. Four arms equal, with five joints each; the fifth arm twice as long, with seven joints. Angles between the arms nearly equal; the odd angle a little larger.

Dimensions.—Radius of the larger odd arm 0.25, of the four smaller arms 0.15; basal breadth 0.035, distal breadth 0.07.

Habitat.—Pacific, central area, Station 274, surface.

4. Pentalastrum cometa, n. sp.

Arms nearly cylindrical, at their obtuse truncated distal end one and a half times as broad as at their base. Posterior odd arm very large, with eleven joints, about three times as long as the two lateral arms (with five joints each) and four times as long as the two anterior arms (with three joints each). Angles between the paired arms different; the two lateral angles smaller than the two posterior, and these smaller than the odd anterior angle.

Dimensions.—Radius of the odd posterior arm 0.5, of the lateral arms 0.25, of the anterior arms 0.18; basal breadth 0.05, distal breadth 0.08.

Habitat.—South Pacific, Station 288, surface.

Genus 241. Pentinastrum,^[67] Haeckel, 1881, Prodromus, p. 461.

Definition.—Porodiscida with five simple, undivided, chambered arms, connected by a patagium.

The genus Pentinastrum differs from the foregoing Pentalastrum only in the development of a patagium or connecticulum between the arms, and bears therefore the same relation to it that Histiastrum does to Stauralastrum, or Hymeniastrum to Dictyastrum.

1. Pentinastrum asteriscus , n. sp. (Pl. 44, fig. 2).

All arms equal, twice as long as broad, at their base two-thirds as broad as at their truncated distal end, which bears a strong, pyramidal, terminal spine. Each arm is divided by five transverse septa into six joints or chambers, and each of these by a radial beam into a pair of chambers. The five radial beams arise from the innermost chamber of the central disk, and end in the five terminal spines. The diameter of the central disk is larger than the length of the arms. The angles between the arms are equal and filled up by an incomplete patagium, so that the whole disk forms a regular pentagon with five concave sides.

Dimensions.—Radius of each arm (without terminal spine) 0.14; breadth at their base 0.02, at their terminal joint 0.03; radius of the central disk 0.06.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

2. Pentinastrum goniaster, n. sp.

? Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pl. xx. fig. 1.

All five arms equal, four times as long as broad, club-shaped, at their globose distal end twice as broad as at their base, and armed with a strong conical terminal spine. Diameter of the central disk equals only one-third of the length of the arms. The articulation of the spongy arms is somewhat obscure. Patagium complete, totally fills up the interbrachial spaces, so that the whole disk forms a regular pentagon with five rectilinear sides, except that the terminal spines project at the corners.

Dimensions.—Radius of each arm 0.18, basal breadth 0.02, distal breadth 0.04; radius of the central disk 0.05.

Habitat.—South Pacific, Station 295, depth 1500 fathoms; also fossil in the rocks of Barbados.

Genus 242. Pentophiastrum,^[68] n. gen.

Definition.—Porodiscida with five forked chambered arms, without a patagium.

The genus Pentophiastrum differs from the two preceding genera by the bifurcation of the five arms, and can be derived either from Pentalastrum by the ramification of the distal ends of the arms, or from the similar Myelastrum by the increase in the number of arms.

1. Pentophiastrum dicranastrum, n. sp.

All five arms equal, with equal angles between them. Each arm in the basal half simple, in the distal half forked; both branches of it equal, with obtuse ends. (This regular species resembles Dicranastrum furcatum, Pl. 47, fig. 2, but with five rays instead of four; also the form of the arms is more slender and the edges smooth.)

Dimensions.—Radius of each arm 0.25, breadth 0.05.

Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.

Subgenus Pentophiastromma, Haeckel.

Definition.—Arms of different size, one odd arm opposite to the angle between both arm-pairs.

2. Pentophiastrum caudatum, n. sp. (Pl. 47, fig. 5).

Arms in pairs different; four arms in the basal half simple, in the distal half forked; the fifth (posterior) odd arm simple, undivided, cylindrical; the anterior pair a little smaller than the posterior; the neighboring branches of the two pairs on each side larger than the two others. Axes of the arms and their branches straight.

Dimensions.—Radius of the arms about 0.5, breadth 0.12.

Habitat.—North Atlantic, Station 353, depth 2965 fathoms.

3. Pentophiastrum forcipatum, n. sp. (Pl. 47, fig. 4).

Arms in pairs different, all in the basal two thirds simple, in the distal third forked. Only in the posterior (odd) arm both branches are equal, in the four others unequal. The common axis of the posterior lateral pair is horizontal, perpendicular to the median line; the axes of the anterior pair are pincer-like, concavely curved towards the median line or principal axis.

Dimensions.—Radius of the arms about 0.5, breadth 0.14.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Genus 243. Hexalastrum,^[69] Haeckel, 1881, Prodromus, p. 461.

Definition.—Porodiscida with six simple chambered arms, without a patagium.

The genus Hexalastrum, together with the following Hexinastrum, encloses those Euchitonida in which the number of the chambered arms surrounding the central disk amounts to six. This is the highest number of these articulated marginal appendages which is reached in any Discoidea. Formerly (1881) in my Prodromus, p. 459, I supposed that the same number was reached also by one Coccodiscid, and called this genus Hexactura. Afterwards I was convinced that this form was also a Hexalastrum.

1. Hexalastrum palmanthum, n. sp.

All six arms equal, with equal angles between them. Each arm club-shaped, three times as long as broad, twice as broad at the thickened distal end as at the base, without a terminal spine.

Dimensions.—Radius of each arm 0.2, basal breadth 0.02, distal breadth 0.06.

Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.

2. Hexalastrum crinanthum, n. sp.

All six arms equal, with equal angles between them. Each arm club-shaped, four times as long as broad, at the egg-shaped distal end three times as broad as in the linear basal part, provided with numerous short conical spines and one longer terminal spine. (Resembles Stauralastrum rhopalophorum, Pl. 45, fig. 1, but with six rays instead of four.)

Dimensions.—Radius of each arm 0.3, basal breadth 0.03, distal breadth 0.08.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

Subgenus Hexalastromma, Haeckel.

Definition.—Arms more or less different in size or form; shell bilateral.

3. Hexalastrum orchidaceum, n. sp. (Pl. 44, fig. 5).

Hexactura orchidacea, Haeckel, 1881, Prodromus, p. 459.

Arms different in length, so that two unequal opposite odd arms determine the main axis, and the four other arms lie on both sides of this as two different pairs. The proportion of their relative length is the following:—anterior lateral arms five, anterior odd arm six; posterior lateral arms seven, posterior odd arm eight. Each arm is club-shaped, two to three times as long as broad, and divided into six to eight joints by five to seven transverse septa; its distal end is armed with a terminal spine and twice as broad as its base.

Dimensions.—Radius of the posterior odd arm 0.4, of the anterior odd arm 0.3; of the posterior lateral pair 0.35, of the anterior lateral pair 0.25; basal breadth 0.08, distal breadth 0.16.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

Genus 244. Hexinastrum,^[70] Haeckel, 1881, Prodromus, p. 461.

Definition.—Porodiscida with six simple, undivided, chambered arms, connected by a patagium.

The genus Hexinastrum differs from its ancestral form Hexalastrum by the development of a patagium between the arms. The only observed species is regular.

1. Hexinastrum geryonidum, n. sp. (Pl. 44, fig. 4).

Hexalastrum geryonidum, Haeckel, 1879, Atlas (pl. xliv. fig. 4).

Disk quite regular with six radii; all six arms of the same size and form, at their broad, convexly rounded, smooth end five times as broad as at their narrow base, and little longer than broad. Each arm is divided by eight transverse septa into nine simple joints or chambers of the same height; the breadth of the distal chambers increases rapidly. The regular, hexagonal, central disk exhibits four concentric rings around the central chamber. Patagium between the arms incomplete, with concavely fluted edge.

Dimensions.—Radius of each arm 0.15, basal breadth 0.016, distal breadth 0.08; radius of the central disk 0.04.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

Family XXII. Pylodiscida, n. fam. (Pl. 48, figs. 12-20).

Definition.—Discoidea without phacoid shell, with flat discoidal shell, in which a simple spherical central chamber is surrounded by one or two concentric triradial girdles; each girdle with three gates, separated by three simple arm-chambers. Surface of the disk with three open or latticed gates on each flat side.

The family Pylodiscida represents a new small but interesting group of Discoidea, which exhibits rather complex affinities to different groups of Sphærellaria. In my Prodromus (1881, p. 464) I had enumerated only two genera of this family, Triopyle and Hexapyle, and had united them with Tetrapyle and allied genera in the family Pylonida. Indeed, the resemblance of skeletal structure in the two groups is very great. The most simple forms of both groups exhibit a simple spherical latticed central chamber, which is surrounded by few latticed chambers of similar size and form, separated by open gates. But in the Pylonida these chambers are opposite in pairs, and form together a complete lattice-girdle around the central chamber, whereas in the Pylodiscida the chambers are not opposite in pairs in one axis, and form therefore only latticed half girdles, which arise from the central chamber like radial arms, and may perhaps better be called "arm-chambers"; their number is constantly three. The free open spaces between these three arm-chambers form three gates, comparable to the two or four gates of Amphipyle, Tetrapyle, &c., and become afterwards closed by lattice-work in a similar way in both groups. A more important difference between them is indicated by the further mode of growth. The Pylonida build new girdles in all three dimensive planes (alternating in the transverse, lateral and sagittal planes); their geometric fundamental form is therefore the "lentellipsis" or the "triaxial ellipsoid." The Pylodiscida, however, grow only at the periphery of the discoidal shell in one single plane (the equatorial plane); their fundamental form is therefore the biconvex lens or the flat disk (a shortened cylinder). This important difference is my deciding motive, in separating the latter from the former and in regarding the Pylodiscida as true Discoidea, the more so as they can easily be derived from Archidiscus, the fundamental and ancestral form of the Porodiscida.

One single form of Archidiscus seems to be of peculiar importance in this relation, viz., Archidiscus hexoniscus (Pl. 48, fig. 10). In this species the simple central chamber is surrounded by a latticed ring or girdle, composed of six equal chambers of the same size and form, all lying in the same plane with the central chamber. In a nearly allied species, viz., Archidiscus pyloniscus, the six ring-chambers are different, three smaller (with denser network) alternating with three larger (of looser network); if we imagine the network of the latter reduced to a marginal bar we get Triopyle, and if also this bar disappear by reduction we get Triolena, the most simple form of the Pylodiscida. Even Archidiscus pyloniscus may possibly represent the same form among the Porodiscida as Triodiscus lenticula among the Pylodiscida; this important form indicates clearly the close affinity of the two families.

If we take the latter, nearly identical form as the common starting point of both families of Cyclodiscaria, then probably Triopyle and Triolene must be regarded as retrograde forms, derived from Triodiscus in the one case, from Archidiscus in the other, by reduction of three interradial arm-chambers, whilst three perradial only remain. But it is also possible that the most simple form, Triolene, originated independently from some Cenosphæra, three simple radial chambers, like the latticed central chamber, being derived from the latter by apposition in three equidistant radii, whilst three other radii between them remained free. In this case the other genera of Pylodiscida are derived from their ancestral form Triolene.

Adopting this latter view, we find that all eight genera of Pylodiscida, here distinguished, may be regarded as following members of a continuous series. If the three simple arm-chambers of Triolene, surrounding the equal central chamber, become united at their distal ends by a concentric equatorial ring, then originates Triopyle; and this graduates into Triodiscus by fenestration of the three open gates between the three latticed arms. Whilst these three genera form together the subfamily Triopylida, a second family, Hexapylida, is composed of three other analogous genera, in which the same process of development becomes repeated.

Pylolena, the most simple form of Hexapylida, arises from Triodiscus by the development of three new arm-chambers (of the second order) which are apposed at the distal end of the three primary arm-chambers (of the first order) in the same radius. If the distal ends of these three secondary arm-chambers become united by a concentric latticed ring or girdle, we get Hexapyle (with six open gates, two in each radius), and if its six gates become afterwards closed by loose lattice-work, we arrive at Pylodiscus (a repetition of Triodiscus).

A third subfamily, Discopylida, is formed by the building of a chambered equatorial girdle around the margin of Pylodiscus. This girdle has quite the same structure as the similar chambered rings or girdles of the Porodiscida and Coccodiscida. Between the two sieve-plates of the disk surface is enclosed a variable number (twelve to twenty-four or more) of chambers, imperfectly separated by radial beams, which connect the margin of the Pylodiscus-shell with an outer peripheral concentric ring. In Discozonium this marginal ring is perfect, whilst in Discopyle it is interrupted by a peculiar large opening, a "marginal osculum" surrounded by a corona of spines, quite the same remarkable formation which we encountered in Ommatodiscus among the Porodiscida.

All Pylodiscida are therefore triradial (with three perradial arms and three interradial gates between them), and many of them have a great resemblance to certain triradial Porodiscida and Spongodiscida, perhaps not only a morphological resemblance, but also a true phylogenetic relation. But it is remarkable that we do not find further forms of development in this family, by multiplication either of the arm-chambers (further growth in the three perradii) or of the concentric chambered rings (in the periphery of the disk margin).

The central capsule of the Pylodiscida is constantly flat, discoidal, and enclosed between the two sieve-plates of the surface. Its form is either circular or triangular.

Synopsis of the Genera of the Pylodiscida.

I. Subfamily Triopylida. Three gates between three simple arm-chambers.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Three gates open, without a barring equatorial girdle,			245. Triolena.
		Three gates barred by a latticed equatorial girdle.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Gate-faces simple,	246. Triopyle.
				Gate-faces latticed,	247. Triodiscus.
II. Subfamily Hexapylida. Six gates between three double arm-chambers (three inner and three outer); no chambered marginal girdle.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Three outer gates open, without a barring equatorial girdle,			248. Pylolena.
		Three outer gates barred by a latticed (second) equatorial girdle.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Both faces of the outer gates simple,	249. Hexapyle.
				Both faces of the outer gates latticed,	250. Pylodiscus.
III. Subfamily Discopylida. Six gates between three double arm-chambers.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	In the equatorial plane on the margin of the Pylodiscus-shell is a chambered equatorial girdle.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	No peculiar osculum on the margin of the disc,	251. Discozonium.
				One peculiar osculum (with a corona of spines) on the margin of the disc,	252. Discopyle.

Subfamily 1. Triopylida, Haeckel.

Definition.—Pylodiscida with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers, which are separated by three notches or gates.

Genus 245. Triolena,^[71] n. gen.

Definition.—Pylodiscida with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers. Notches between the three arms open.

The genus Triolena is the most simple form of all Pylodiscida, and must be regarded as their common ancestral form, from an ontogenetic as well as a phylogenetic point of view. The small shell is composed of a simple, spherical or lenticular, latticed, central chamber, and of three simple, surrounding equal arms, which are also simple latticed chambers, lie in the equatorial plane, and are separated by three equal angles or open gates.

1. Triolena primordialis, n. sp. (Pl. 48, fig. 12).

Arm-chambers trapezoid, nearly square, of the same size as the circular, lenticular, primordial, central chamber. Surface of the disk smooth.

Dimensions.—Diameter of the shell 0.045, of the central chamber 0.015, of each arm 0.015.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

2. Triolena tribelone, n. sp.

Arm-chambers lanceolate, of the same breadth as and twice the length of the triangular, central chamber; at the pointed end of each arm is a conical terminal spine (in the equatorial plane). Surface of the disk thorny.

Dimensions.—Diameter of the shell 0.05, of the central chamber 0.015; length of the arms 0.02, breadth 0.016.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

3. Triolena trispinosa, n. sp.

Arm-chambers ovate, in the basal half nearly as broad as the hexagonal central chamber, at the pointed distal end with a strong conical radial spine of double the length. Surface rough.

Dimensions.—Diameter of the shell 0.055, of the central chamber 0.02.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

4. Triolena hexabelone, n. sp.

Arm-chambers nearly triangular, at the base half as broad as the hexagonal central chamber, at the truncate distal end one and a half times as broad, and armed with two radial conical spines (in the equatorial plane). Surface of the disk smooth.

Dimensions.—Diameter of the shell 0.06, of the central chamber 0.02.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

5. Triolena trigonalis, n. sp.

Arm-chambers nearly triangular, at the base half as broad as the circular central chamber, at the concave lunulate distal end twice as broad, and armed with four conical radial spines (two on each side of the equatorial plane). Surface thorny.

Dimensions.—Diameter of the shell 0.05, of the central chamber 0.015.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 246. Triopyle,^[72] Haeckel, 1881, Prodromus, p. 464.

Definition.—Pylodiscida with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers. Notches between the three arms transformed into gates by a connecting equatorial girdle.

The genus Triopyle differs from the preceding Triolene in the development of a simple ring or latticed equatorial girdle, which connects the distal ends of the three arm-chambers, and transforms the open notches between them into three gates. The ring may be circular, triangular, or hexagonal.

1. Triopyle circulus, n. sp.

Disk circular, three times as broad as the hexagonal central chamber. Three arm-chambers trapezoidal, at the convex distal end as broad, at the base half as broad as the three circular gates between them. Surface smooth. No marginal spines on the girdle.

Dimensions.—Diameter of the disk 0.045, of the gates 0.015.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

2. Triopyle hexagona, n. sp. (Pl. 48, fig. 13).

Disk hexagonal, three times as broad as the circular central chamber. Three arm-chambers trapezoidal, at the truncated distal end as broad, at the base half as broad as the three triangular gates between them. Surface smooth. No marginal spines.

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

3. Triopyle trigona, n. sp.

Disk triangular, four times as broad as the circular central chamber. Three arm-chambers nearly triangular, at the narrow base half as broad, at the distal end twice as broad as the circular or roundish gates. Surface smooth. On the margin (in the equatorial plane) three strong pyramidal spines (at the end of the arms).

Dimensions.—Diameter of the disk 0.04, of the gates 0.015.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

4. Triopyle cordigera, n. sp.

Disk hexagonal, four times as broad as the hexagonal central chamber. Three arm-chambers triangular, at the base half as broad as at the truncated distal end, about the same size as the three heart-shaped gates. On the six corners of the margin (which forms a regular hexagon) are six pyramidal radial spines, as prolongations of the arm-edges.

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

Habitat.—Indian Ocean, Ceylon, surface, Haeckel.

5. Triopyle renigera, n. sp.

Disk hexagonal, five times as broad as the circular central chamber. Three arm-chambers trapezoidal, at the base one-third, at the distal end two-thirds as broad as the three kidney-shaped gates. On the six corners of the margin (which forms an irregular hexagon) six conical radial spines, as prolongations of the arm-edges.

Dimensions.—Diameter of the disk 0.06, of the gates 0.02.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

6. Triopyle spinigera, n. sp.

Disk roundish, triangular, four times as broad as the triangular central chamber, which is armed with three radial spines between the arms. Arm-chambers club-shaped, at the narrow base one-fourth, at the distal end half as broad as the square gates. On the margin twelve large conical spines, two opposite on each face of the distal end of each arm-edge. Three smaller radial spines on the three corners of the girdle (in the same interradial meridian planes as the three spines of the central chamber). Compare Triodiscus spinosus.

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Genus 247. Triodiscus,^[73] n. sp.

Definition.—Pylodiscida with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers. Notches between the three arms closed by lattice-work and by an equatorial girdle.

The genus Triodiscus differs from the preceding Triopyle in the development of loose lattice-work on both sides of the discoidal shell. This network closes the gates and transforms the whole shell into a fenestrated lens. The singular species of Triodiscus correspond to certain species of Triopyle.

1. Triodiscus lenticula, n. sp.

Disk circular, lenticular, three times as broad as the central chamber. Three arm-chambers trapezoidal, of the same size and form as the three gates between them, which are closed by a loose delicate network (differs from Triopyle circulus by the production of the two convex latticed plates, which envelop the whole lens). Margin smooth.

Dimensions.—Diameter of the disk 0.045, of the gates 0.015.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

2. Triodiscus trigonus, n. sp.

Disk triangular, four times as broad as the central chamber. Three arm-chambers at the base half as broad, at the distal end twice as broad as the roundish gates. Surface smooth. On the three corners of the margin (in the arm-radius) three strong spines. (Differs from Triopyle trigona only in the loose framework closing the gates.)

Dimensions.—Diameter of the disk 0.04, of the gates 0.015.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

3. Triodiscus spinosus, n. sp. (Pl. 48, fig. 14).

Disk subcircular, four times as broad as the triangular central chamber. Three arm-chambers club-shaped, at the base one-third, at the distal end two-thirds as broad as the semicircular gates. Surface thorny. On the margin fifteen larger radial spines, three on the corners of the disk (in the radius of the gates), twelve on the two faces of the arms ends (two opposite on the edge of each end.) (Differs from Triopyle spinigera mainly by the delicate hexagonal network closing the gates.)

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

Habitat.—North Atlantic, Canary Islands (Lanzerote, Haeckel).

Subfamily 2. Hexapylida, Haeckel.

Definition.—Pylodiscida with triopyle-shaped medullary shell, surrounded by three distal arm-chambers, which are separated by three open notches or gates.

Genus 248. Pylolena,^[74] n. gen.

Definition.—Pylodiscida with triopyle-shaped medullary shell, surrounded by three distal arm-chambers. Notches between the three arms open.

The genus Pylolena opens the series of the Hexapylida, or of those Pylodiscida in which the centre of the shell is formed by a tri-radiated medullary shell like Triopyle. In the equatorial plane of this triopyle-shaped disk are developed on its margin three distal arm chambers, as prolongations of the three arms of Triopyle, but much larger. In Pylolene the three angles or notches between the distal arms remain open, repeating the form of Triolene.

1. Pylolena inermis, n. sp.

Arms club-shaped, at the base half as broad, at the rounded distal end as broad as the triopyle-shaped medullary shell. Surface and margin smooth.

Dimensions.—Diameter of the cortical shell 0.15, of the medullary shell 0.05.

Habitat.—Equatorial Atlantic, Station 347, surface; Central Pacific, Station 272, surface.

2. Pylolena armata, n. sp. (Pl. 48, fig. 15).

Arms trapezoid, at the base half as broad, at the distal end twice as broad as the triopyle-shaped medullary shell. Surface and margin thorny. Twelve strong conical spines at the distal end of the three arms, two opposite on both faces of the arm-edges.

Dimensions.—Diameter of the cortical shell 0.2, of the medullary shell 0.06.

Habitat.—South Atlantic, Station 325, surface.

Genus 249. Hexapyle,^[75] Haeckel, 1881, Prodromus, p. 464.

Definition.—Pylodiscida with triopyle-shaped medullary shell, surrounded by three distal arm-chambers. Notches between the three arms transformed into gates by a connecting equatorial girdle.

The genus Hexapyle differs from the preceding Pylolene in the development of an equatorial ring or latticed girdle, which connects the free extremities of the three distal ends and transforms the open notches between them into gates. It simulates therefore the formation of Triopyle, from which it differs by duplication of the arm-joints and of the gates (in each radius occur one proximal and one distal gate).

1. Hexapyle triangula, n. sp.

Cortical shell triangular, with three rounded corners, three times as broad as the triangular triopyle-shaped medullary shell. Surface smooth or rough, but not spiny. Three arms two-thirds as broad as the three egg-shaped gates of each side.

Dimensions.—Diameter of the cortical shell (or length of one side of the triangle) 0.15, of the medullary shell 0.05; breadth of the gates 0.06, of the bridges between them 0.04.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

2. Hexapyle sexangula, n. sp.

Cortical shell hexagonal, with six equal sides, four times as broad as the triangular triopyle-shaped medullary shell. Surface rough, but not spiny. Three arms (on their smallest part) half as broad as the three triangular gates (on their broadest part).

Dimensions.—Diameter of the cortical shell 0.16, of the medullary shell 0.04; breadth of the gates 0.06, of the bridges 0.03.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

3. Hexapyle circularis, n. sp.

Cortical shell circular, four times as broad as the triangular, Triopyle-shaped medullary shell. Surface smooth. Three arms half as broad as the three kidney-shaped gates on each side of the shell.

Dimensions.—Diameter of the cortical shell 0.2, of the medullary shell 0.05; breadth of the gates 0.08, of the bridges between them 0.04.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

4. Hexapyle triacantha, n. sp.

Cortical shell triangular, thorny, with three pointed corners, prolonged into three strong conical radial spines; its diameter four times as great as that of the medullary shell. Three arms of the same breadth as the three egg-shaped gates of each side.

Dimensions.—Diameter of the cortical shell (or length of one side of the triangle, without spines) 0.2, of the medullary shell 0.05; breadth of the gates and of the bridges between them 0.06.

Habitat.—Indian Ocean, surface; Madagascar, Rabbe.

5. Hexapyle hexacantha, n. sp.

Cortical shell hexagonal, thorny, three times as broad as the medullary shell. Six stronger conical radial spines on the six corners at equal distances, lying in the equatorial plane of the disk. Three half girdles half as broad as the three triangular gates of each side.

Dimensions.—Diameter of the cortical shell 0.15, of the medullary shell 0.05; breadth of the gates 0.05, of the bridges 0.025.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

6. Hexapyle dodecantha, n. sp. (Pl. 48, fig. 16).

Cortical shell triangular, thorny, with rounded corners, three and a half times as broad as the medullary shell. Twelve stronger radial spines, six opposite in pairs on each side of the discoidal shell, as prolongations of the lateral edges of the triangular gates, which are about the same breadth as the half girdles between them.

Dimensions.—Diameter of the cortical shell 0.21, of the medullary shell 0.06; breadth of the gates and of the bridges 0.06.

Habitat.—Pacific, central area, Station 270, surface.

7. Hexapyle polyacantha, n. sp.

Cortical shell circular, thorny, with a circle of numerous conical radial spines in the periphery; its diameter nearly three times as great as that of the medullary shell. Three half-girdles half as broad as the three kidney-shaped gates on each side of the discoidal shell.

Dimensions.—Diameter of the cortical shell 0.11, of the medullary shell 0.04; breadth of the gates 0.04, of the bridges between them 0.02.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Genus 250. Pylodiscus,^[76] n. gen.

Definition.—Pylodiscida with Triopyle-shaped medullary shell, surrounded by three distal arm-chambers. Notches between the three arms closed by lattice-work and by an equatorial girdle.

The genus Pylodiscus differs from Hexapyle in the development of two convex plates of lattice-work, which close the six open gates and transform the disk into a biconvex fenestrated lens. Pylodiscus simulates therefore the characteristic form of Triodiscus; but whilst in the latter we find only three arm-joints and three simple gates, their number is doubled in the former.

1. Pylodiscus triangularis, n. sp. (Pl. 48, fig. 17).

Cortical shell triangular, with rounded corners, three times as broad as the triangular, Triopyle-shaped medullary shell. Three arms about as broad as the three egg-shaped gates between them. (Differs from Hexapyle triangula only by the delicate network of both triangular convex covering plates, which close the open gates.) Six larger and many smaller spines on the margin of the disk.

Dimensions.—Diameter of the disk 0.15, of the gates 0.05.

Habitat.—Pacific, central area, Station 270, depth 2925 fathoms.

2. Pylodiscus sexangularis, n. sp.

Cortical shell hexangular, equilateral, four times as broad as the circular, Triopyle-shaped medullary shell. Surface spiny. Three arms nearly of the same form and size as the three triangular gates between them. (Similar to Hexapyle sexangularis, but differing in the irregular loose network closing the gates.)

Dimensions.—Diameter of the disk 0.18, of the gates 0.06.

Habitat.—North Pacific, south of Japan, Station 237, surface

3. Pylodiscus cardiopylus, n. sp.

Cortical shell hexangular, equilateral, five times as broad as the triangular, Triopyle-shaped medullary shell. Surface smooth. Three arms triangular, at the distal end as broad as the three heart-shaped gates. On the margin six strong pyramidal spines in the equatorial plane (adradial, as prolongations of the lateral arm-edges).

Dimensions.—Diameter of the disk 0.15, of the gates 0.05.

Habitat.—Indian Ocean, Sunda Strait, Rabbe.

4. Pylodiscus nephropylus, n. sp.

Cortical shell circular, three times as broad as the circular, Triopyle-shaped medullary shell. Surface spiny. Three arms trapezoidal, half as broad as the three kidney-shaped gates. On the margin twelve stronger, conical, radial spines, opposite in pairs on both sides of the disk, disposed in six pairs at the distal end of the arms.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.06.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

Subfamily 3. Discopylida, Haeckel.

Definition.—Pylodiscida with Triopyle-shaped medullary shell and Pylodiscus-shaped cortical shell, which is surrounded by a marginal chambered equatorial girdle.

Genus 251. Discozonium,^[77] n. gen.

Definition.—Pylodiscida with Triopyle-shaped medullary shell and Pylodiscus-shaped cortical shell, which is surrounded by an equatorial chambered girdle. No peculiar osculum on the margin of the disk.

The genus Discozonium and the following Discopyle make up together the small group of the Discopylida, or those Pylodiscida in which a discoidal shell like Pylodiscus is surrounded by a marginal equatorial girdle; this girdle is divided into twelve to twenty-four or more chambers by radial beams, which are the external prolongations of the radial marginal spines of Pylodiscus. The latter genus bears therefore to Discozonium the same relation as Sethodiscus in the other Discoidea does to Lithocyclia, or Phacodiscus to Coccodiscus.

1. Discozonium cyclonium, n. sp.

Disk circular, lenticular, with smooth margin, three times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell kidney-shaped, twice as broad as the three arms. Chambered equatorial girdle with twenty to twenty-four subregular chambers (similar to Discopyle osculata, Pl. 48, fig. 19, but without any marginal osculum).

Dimensions.—Diameter of the disk 0.2, of the cortical shell 0.14, of the medullary shell 0.07.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

2. Discozonium trigonium, n. sp.

Disk triangular, with thorny margin, four times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell egg-shaped, scarcely as broad as the three arms. Chambered equatorial girdle with twenty-four to thirty irregular chambers.

Dimensions.—Diameter of the disk 0.24, of the cortical shell 0.2, of the medullary shell 0.06.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

3. Discozonium hexagonium, n. sp. (Pl. 48, fig. 18).

Disk hexagonal, with spiny margin, four times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell kidney-shaped, one and a half times as broad as the arms. Chambered equatorial girdle with twelve large regular chambers; the radial beams between them are prolonged into twelve strong pyramidal marginal spines (three perradial on the ends of the arms, three interradial on the radii of the gates, six adradial between the former and latter).

Dimensions.—Diameter of the disk 0.2, of the cortical shell 0.12, of the medullary shell 0.05.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 252. Discopyle,^[78] n. gen.

Definition.—Pylodiscida with Triopyle-shaped medullary shell and Pylodiscus-shaped cortical shell, which is surrounded by an equatorial chambered girdle. One peculiar osculum, surrounded by a corona of spines, on the margin of the disk.

The genus Discopyle differs from the preceding genus Discozonium in the development of a peculiar marginal osculum, and bears therefore to it the same relation as, in the Porodiscida, Ommatodiscus does to Porodiscus (compare above, p. 500). This peculiar osculum is here also surrounded by a corona of spines, and serves probably for the exit or outlet of a bunch of pseudopodia or a "sarcode-flagellum." Only two species of Discopyle have been observed, which represent perhaps better two different genera; in one species the disk is circular, in the other elliptical. In this latter the osculum lies on one pole of the main axis.

1. Discopyle osculata, n. sp. (Pl. 48, fig. 19).

Disk circular with spiny margin, three times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell kidney-shaped, on the inside with an interradial spine, twice as broad as the three pentagonal arms. Chambered equatorial girdle with twenty-four subregular chambers, in the radius of one odd gate with a large marginal osculum, which is as broad as the medullary shell, and surrounded by a dense corona of twenty to thirty strong conical spines.

Dimensions.—Diameter of the disk 0.15, of the cortical shell 0.1, of the medullary shell 0.05, of the marginal osculum 0.06.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

2. Discopyle elliptica, n. sp. (Pl. 48, fig. 20).

Disk elliptical, four-fifths as broad as long, with spiny margin, three times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell roundish, on the inside with an interradial spine, little broader than the quadrangular arms. Chambered equatorial girdle with twenty to thirty irregular chambers, on one pole of the main axis with a large marginal osculum, which is one-third as broad as the length of the main axis, and armed with a corona of twenty to thirty short conical spines. The osculum does not correspond to a certain radius.

Dimensions.—Diameter of the disk 0.15, of the cortical shell 0.08, of the medullary shell 0.04, of the marginal osculum 0.05.

Habitat.—Central Pacific, Station 267, depth 2700 fathoms.

Family XXIII. Spongodiscida, Haeckel (Pl. 41, fig. 11).

Spongodiscida et Spongocyclida, Haeckel, 1862, Monogr. d. Radiol.,
⁠pp. 452, 460, 469.
Spongodiscida, Haeckel, 1881, Prodromus, p. 461.
Calodictya, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss.
⁠Berlin, p. 53 (partim).

Definition.—Discoidea without a phacoid shell, with a flat discoidal shell, in which a simple spherical central chamber is surrounded by an irregular spongy framework (sometimes with concentric rings around the central chamber). Surface of the disk quite spongy, without porous sieve-plates.

The family Spongodiscida is the sixth and last family of the Discoidea, and bears to the other families of this group the same relation as the family Spongosphærida does to the other Sphæroidea, or the Spongurida to the other Prunoidea. Its characteristic structure consists in the irregular spongy framework of the disk, and mainly in the rough, irregular shape of its spongy surface, which is never covered with porous plates (neither phacoid shell nor corresponding sieve-plates), as in all other Discoidea. Of course a little spongy structure occurs also in many Porodiscida and even in some Coccodiscida (principally in the peripheral part of the disk or its chambered arms); but both flat (or convex) surfaces of the disk (at least in the central part) remain here constantly as simple lattice-plates, whilst in all Spongodiscida the whole surface of the disk is spongy.

When I constituted the family Spongodiscida in my Monograph (1862, pp. 452, 460) I had separated from them the Spongocyclida, exhibiting in the central part of the disk a more or less distinct concentric arrangement of the spongy chambers, whilst in the former the delicate spongy framework is quite irregular, composed of branched siliceous threads, connected and interwoven in all directions. But in all Spongocyclida the whole surface of the spongy disk is quite as irregularly rough and deprived of smooth sieve-plates as in all true Spongodiscida, and the more or less concentric structure of the central part of the disk in the former (very variable and often scarcely able to be recognised) seems not sufficient to separate both groups; even the single genera cannot be sufficiently separated by this character. I now therefore give up entirely the group of Spongocyclida (as already done in my Prodromus, 1881). Nevertheless the concentric annular structure in the dark central part of some Spongodiscida is very interesting as transition to the Porodiscida; it indicates already that the former are derived from the latter. Even the single genera in both families are corresponding.

In the new system of "Polycystina," which Ehrenberg gave, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, p. 157), are enumerated under the Calodictya four genera "with spongy disk," viz., Spongodiscus, Rhopalodictyum, Dictyocoryne, Spongaster. Indeed these four genera, which I here retain, are true Spongodiscida, and must be separated from the other Calodictya, the greater part of which are Porodiscida. The number of species of true Spongodiscida now amounts to sixty-seven, which I dispose in thirteen genera.

The whole family may be divided into three subfamilies. The first of these are the Spongophacida (corresponding to the Trematodiscida among the Porodiscida), in which the circular margin of the spongy disk bears no radial appendages; either the margin is quite simple, spongy (Spongodiscus), or surrounded by a hyaline, solid, or porous equatorial girdle (Spongophacus). The disk is either more lenticular (biconvex) or more flat discoidal (a shortened cylinder), rarely a little biconcave (thicker at the margin than in the centre). The spongy framework of the solid disk is either quite irregular (Spongodisculus), or in the central part with concentric circular rings (Spongocyclia), or in the central part spirally convoluted (Spongospira).

The second subfamily, Spongotrochida, corresponds to the Stylodictyida (among the Porodiscida), and is distinguished by solid radial spines on the margin of the disk, disposed in the equatorial plane either irregularly or regularly (after the same order as in the other families of Discoidea).

The third subfamily, Spongobrachida, correspond perfectly to the Euchitonida (among the Porodiscida), bearing on the disk-margin two, three, or four spongy arms, commonly disposed regularly in the equatorial plane. Here also occurs the peculiar formation of a "patagium," or of an interbrachial spongy framework different from that of the arms, which connects the arms like a web-membrane in the equatorial plane.

The spongy framework exhibits in all these Spongodiscida no remarkable differences, being everywhere composed of fine branched solid siliceous threads, interwoven in all directions, with irregular meshes of very different size.

The central capsule of all Spongodiscida is filled up with the same spongy framework which covers also both its sides. It grows according to the enveloping skeleton, but remains constantly smaller. The form of the central capsule is circular (lenticular or discoidal) in the Spongophacida and Spongotrochida, whilst in the Spongobrachida it enters into the radial spongy arms, developed from the margin of the spongy disk.

Synopsis of the Genera of the Spongodiscida.

III. Subfamily Spongophacida. Spongy disk without radial appendages.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Spongy disk with simple margin (without peculiar equatorial girdle),			253. Spongodiscus.
		Spongy disk with a peculiar (solid or porous) equatorial girdle,			254. Spongophacus.
III. Subfamily Spongotrochida. Spongy disk with solid radial spines on the margin (in the equatorial plane).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Few (two, three, or four) radial spines regularly disposed.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Two opposite spines,	255. Spongolonche.
				Three marginal spines,	256. Spongotripus.
				Four crossed spines,	257. Spongostaurus.
		Numerous (five to ten or more) radial spines, often irregularly disposed.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Spines only on the margin (equatorial),	258. Stylotrochus.
				Spines on both sides of the disk,	259. Spongotrochus.
III. Subfamily Spongobrachida. Spongy disk with spongy radial arms on the margin (in the equatorial plane).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Two arms, opposite in one axis.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without a patagium,	260. Spongolena.
				With a patagium,	261. Spongobrachium.
		Three arms on the margin.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without a patagium,	262. Rhopalodictyum.
				With a patagium,	263. Dictyocoryne.
		Four arms in cross form.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without a patagium,	264. Spongasteriscus.
				With a patagium,	265. Spongaster.

Subfamily 1. Spongophacida, Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with a simple circular disk, without radial appendages on the margin (neither solid spines nor chambered arms).

Genus 253. Spongodiscus,^[79] Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 237.

Definition.—Spongodiscida with a simple circular disk, without radial appendages and without an equatorial girdle on the margin.

The genus Spongodiscus represents the most simple and primitive form of the Spongodiscida, or of those Discoidea in which the central disk is more or less spongy, composed of an irregular fine framework. In my Monograph (1862, pp. 452, 460, 469) I had separated the true Spongodiscus (first described by Ehrenberg, loc. cit.) and the Spongocyclia; the former being characterised by the irregular spongy framework of the whole disk, whilst in the latter this framework includes in the central part some concentric circular rings (approaching Porodiscus). In the same way afterwards Stöhr (1880, loc. cit.) separated the genus Spongospira as spongy disks, which include in the central part some spiral convolutions. But as these differences are rather inconstant and not sharply discernible, I think it now better to regard these three forms as subgenera of Spongodiscus. All three have the common simple circular disk, without any marginal appendages.

Subgenus 1. Spongodisculus, Haeckel.

Definition.—Spongy framework of the disk quite irregular, without concentric rings or spiral convolutions.

1. Spongodiscus mediterraneus, Haeckel.

Spongodiscus mediterraneus, Haeckel, 1862, Monogr. d. Radiol., p. 461, Taf. xii. figs. 14, 15.

Spongy disk plain on both sides, with quite an irregular framework, without concentric rings and without radial piercing beams. Texture everywhere uniform; meshes eight to ten times as broad as the bars.

Dimensions.—Diameter of the disk 0.08 to 0.24, of the meshes 0.005 to 0.008.

Habitat.—Mediterranean (Messina), Haeckel; also fossil in the Tertiary rocks of Sicily (Grotte), Stöhr.

2. Spongodiscus radiatus, n. sp.

Spongy disk plain on both sides, with quite irregular framework, without concentric rings, but with numerous piercing radial beams which are not prolonged into marginal spines. Texture everywhere uniform; meshes once and a half to twice as broad as the bars.

Dimensions.—Diameter of the disk 0.12 to 0.15, of the meshes 0.002 to 0.003.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

3. Spongodiscus resurgens, Ehrenberg.

Spongodiscus resurgens, Ehrenberg, 1854, Mikrogeol., Taf. xxxvB. B. iv., fig. 16. Spongodiscus resurgens, Stöhr, 1880, Palæontogr., xxvi. p. 117, Taf. vi. fig. 11.

Spongy disk lenticular, biconvex, in the darker centre much thicker than towards the thin periphery, with an irregular framework, without concentric rings, but with numerous piercing radial beams. Texture equal; meshes three to four times as broad as the bars.

Dimensions.—Diameter of the disk 0.1 to 0.3, of the meshes 0.003 to 0.006.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in the Tertiary rocks of Sicily and Barbados.

4. Spongodiscus favus, Ehrenberg.

Spongodiscus favus, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 301.

Spongy disk lenticular, biconvex, in the darker centre much thicker than towards the periphery, with an irregular framework, without concentric rings. Texture different, in the outer half with numerous radial beams and loose network, the meshes of which are three to four times as large as in the darker and denser framework of the centre.

Dimensions.—Diameter of the disk 0.2, of the outer meshes 0.008 to 0.012, of the inner meshes 0.002 to 0.003.

Habitat.—North Atlantic, Greenland, Færöe Channel (John Murray), surface.

5. Spongodiscus biconcavus, n. sp.

Spongy disk biconcave, in the peripheral, ring-like, thickened part twice as thick as in the hollowed central part, with an irregular framework, without concentric rings. Texture different, in the outer half looser than in the inner, darker part; meshes of the outer part five to six times, of the inner twice to three times, as broad as the bars.

Dimensions.—Diameter of the disk 0.25, of the outer meshes 0.01 to 0.012, of the inner 0.004 to 0.006.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Subgenus 2. Spongocyclia, Haeckel, 1862, Monogr. d. Radiol., p. 469.

Definition.—Spongy framework of the disk in the inner part with concentric, circular rings, in the outer part irregular.

6. Spongodiscus cycloides, Haeckel.

Spongodiscus cycloides, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 843. Spongocyclia cycloides, Haeckel, 1862, Monogr. d. Radiol., p. 469, Taf. xxviii. fig. 1.

Spongy disk on both sides plain, in the central part with five to ten concentric, circular rings, in the peripheral part quite irregularly and densely spongy. Meshes twice to four times as broad as the bars.

Dimensions.—Diameter of the disk 0.1 to 0.2, of the meshes 0.003 to 0.006.

Habitat.—Mediterranean (Messina), North Atlantic (Canary Islands).

7. Spongodiscus spongocyclia, Haeckel.

Spongocyclia triangularis, Stöhr, 1880, Palæontogr., vol. xxvi. p. 119, Taf. vii. fig. 5.

Spongy disk lenticular, in the thicker central part with eleven to twelve circular, concentric rings, in the thinner, peripheral zone irregularly spongy. Meshes twice to four times as broad as the bars. (The triangular form in the specimen figured by Stöhr is accidental, produced by the broken margin.)

Dimensions.—Diameter of the disk 0.2 to 0.3, of the meshes 0.006 to 0.008.

Habitat.—Fossil in Tertiary rocks of Barbados (Haeckel) and Sicily (Stöhr).

Subgenus 3. Spongospira, Stöhr, 1880, Palæontogr., vol xxvi. p. 120.

Definition.—Spongy framework of the disk in the inner part with spiral convolutions, in the outer part irregular.

8. Spongodiscus florealis, Haeckel.

Spongospira florealis, Stöhr, 1880, Palæontogr., vol. xxvi. p. 120, Taf. vii. fig. 6.

Spongy disk lenticular, in the thicker central part with five to six spiral convolutions, in the outer peripheral zone irregularly spongy. No radial beams piercing the framework. Meshes three to four times as broad as the bars.

Dimensions.—Diameter of the disk 0.26, of the meshes 0.006 to 0.008.

Habitat.—Fossil in Tertiary rocks of Sicily (Grotte), Stöhr.

9. Spongodiscus spiralis, n. sp.

Spongospira spiralis, Haeckel, 1881, Prodromus.

Spongy disk on both sides plain, with twelve to sixteen spiral convolutions in the central part, with irregular, spongy framework in the outer part, pierced by numerous interrupted radial beams. Meshes five to six times as broad as the bars.

Dimensions.—Diameter of the disk 0.2 to 0.3, of the meshes 0.01 to 0.012.

Habitat.—Antarctic Ocean, Station 157, depth 1950 fathoms.

Genus 254. Spongophacus,^[80] Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with a simple circular disk, without radial appendages, on the margin surrounded by a thin porous or solid equatorial girdle.

The genus Spongophacus, represented hitherto only by a single but interesting species, differs from Spongodiscus by the peculiar girdle which surrounds the margin of the disk in the equatorial plane. It simulates the same formation as Perichlamydium in the Porodiscida, and resembles also Periphæna, &c., in the Phacodiscida.

1. Spongophacus periphæna, n. sp.

Spongy disk lenticular, with an irregular, dense framework, in the centre darker than in the peripheral part. Margin of the disk very thin, surrounded by a broad, circular girdle, lying in the equatorial plane, about as broad as the half radius of the spongy disk. The inner part of the girdle is perforated by numerous irregular, small pores, which pass over gradually into the spongy meshes; the outer part is quite homogeneous, solid, transparent, with an extremely thin margin.

Dimensions.—Diameter of the disk 0.2; breadth of the girdle 0.05.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Subfamily 2. Spongotrochida, Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with a circular disk, the margin of which is armed with solid radial spines, situated in the equatorial plane (rarely also on both sides of the disk with radial spines).

Genus 255. Spongolonche,^[81] Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with two solid marginal spines, opposite in one equatorial diameter of the disk.

The genus Spongolonche opens the series of the Spongotrochida, or of those Spongodiscida in which the margin of the disk is armed with solid radial spines, situated in the equatorial plane. Spongolonche possesses only two such spines, opposite in one equatorial diameter of the disk; it corresponds therefore to Stylocyclia among the Coccodiscida, to Xiphodictya among the Porodiscida.

1. Spongolonche conostyla, n. sp..

Spongy disk circular, with irregular framework, without concentric rings. Both opposite radial spines conical, about as long as the radius of the disk, and four times as long as broad at the base. Margin of the disk nearly smooth.

Dimensions.—Diameter of the disk 0.16; length of the radial spines 0.18, basal thickness 0.045.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

2. Spongolonche amphistyla, n. sp.

Spongy disk circular, with four to six concentric rings in the inner part, with quite an irregular framework in the outer part. Both opposite radial spines cylindrical, twice to three times as long as the diameter of the disk, at the base about as broad as two meshes of the framework. Margin of the disk ciliated.

Dimensions.—Diameter of the disk 0.2; length of the radial spines 0.4 to 0.6, basal thickness 0.01.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Genus 256. Spongotripus,^[82] Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with three solid radial spines on the margin of the circular or triangular disk.

The genus Spongotripus is characterised by three marginal spines, which are commonly regularly disposed, more rarely in a bilateral or an irregular manner. It corresponds to Trigonocyclia among the Coccodiscida, to Tripodictya among the Porodiscida.

Subgenus 1. Spongotripodiscus, Haeckel.

Definition.—Radial spines of equal size and distance; triangle regular.

1. Spongotripus regularis, n. sp.

Spongy disk circular; three radial spines on its margin of equal size and equidistant, strong, conical, about as long as the diameter of the disk, and five times as long as broad at the base.

Dimensions.—Diameter of the disk 0.15; length of the spines 0.16, basal breadth 0.03.

Habitat.—Pacific, central area, Station 272, surface.

2. Spongotripus neumayri, Haeckel.

Spongechinus neumayri, Dunikowski, 1882, Denskchr. d. k. Akad. d. Wiss. Wien, xlv. p. 28, Taf. v. fig. 59.

Spongy disk circular, nearly spherical; three radial spines on its margin of equal size and equidistant, pyramidal, nearly as long as the diameter of the disk, and three times as long as broad at the base.

Dimensions.—Diameter of the disk 0.15 to 0.2; length of the spines 0.11, basal breadth 0.04.

Habitat.—Fossil in the Jura of the Alps and in Tertiary rocks of Barbados.

3. Spongotripus strepsiceros, n. sp.

Spongy disk circular; three radial spines on its margin of equal size and equidistant, angular, twice as long as the diameter of the disk, spirally twisted like the horns of Antilope strepsiceros.

Dimensions.—Diameter of the disk 0.15; length of the spines 0.3, basal breadth 0.02.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

Subgenus 2. Spongotripodium, Haeckel.

Definition.—Radial spines of different size or at different distances; triangle either isosceles or irregular.

4. Spongotripus ypsilon, n. sp.

Spongy disk triangular, isosceles, with convex sides; three spines angular, of different size and at different distances; the odd spine straight and twice as long as the two paired spines, which are more approximated and curved concavely one to the other, like .

Dimensions.—Diameter of the disk 0.12; length of the odd spine 0.2, of the paired spines 0.1, basal breadth 0.04.

Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.

5. Spongotripus irregularis, n. sp.

Spongy disk circular; three spines conical, irregularly curved, all three of different size, and at irregular distances; once to three times as long as the diameter of the disk; margin of the disk thorny.

Dimensions.—Diameter of the disk 0.1; length of the spines 0.1 to 0.3, basal breadth 0.05.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

Genus 257. Spongostaurus,^[83] Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with four solid radial spines on the margin of the circular or square disk, commonly crossed in two equatorial diameters perpendicular one to another.

The genus Staurodictya exhibits four marginal spines in cross form. Commonly the cross is regular and rectangular, the four spines being opposite in pairs in two perpendicular diameters; sometimes more or less irregular. The genus repeats Staurodictya among the Porodiscida, Staurocyclia among the Coccodiscida.

1. Spongostaurus cruciatus, n. sp.

Spongy disk circular; four radial spines on its margin opposite in two crossed equatorial diameters, perpendicular one to another, conical, about as long as the diameter of the disk.

Dimensions.—Diameter of the disk 0.16; length of the spines 0.18, basal breadth 0.04.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

2. Spongostaurus serratus, n. sp.

Spongy disk circular; four crossed radial spines very large, twice to three times as long as the diameter of the central disk, serrated on both edges, with two rows of strong conical perpendicular teeth (similar to the saw of Pristis antiquorum).

Dimensions.—Diameter of the disk 0.1; length of the spines 0.2 to 0.3, breadth 0.02.

Habitat.—Indian Ocean, Madagascar, Rabbe, surface.

3. Spongostaurus hastatus, n. sp.

Spongy disk square, with concave sides; four crossed radial spines cylindrical, on the broader distal end spear-shaped or nearly lanceolate, one and a half times as long as the diameter of the disk.

Dimensions.—Diameter of the disk 0.13; length of the spines 0.2, basal breadth 0.01, distal breadth 0.03.

Habitat.—Tropical Atlantic, Station 347, surface.

4. Spongostaurus quadratus, n. sp.

Spongy disk square, with rectilinear sides; four crossed radial spines pyramidal, arising from the corners of the square, about as long as its half diagonal.

Dimensions.—Diameter of the disk 0.16; length of the spines 0.08, basal breadth 0.02.

Habitat.—Pacific, central area, Station 271, surface.

Genus 258. Stylotrochus,^[84] Haeckel, 1862, Monogr. d. Radiol., p. 463.

Definition.—Spongodiscida with numerous solid radial spines on the margin of the disk (five to ten or more), all situated in the equatorial plane.

The genus Stylotrochus comprises those Spongodiscida in which the margin of the circular disk bears numerous radial spines. All these spines lie in the same equatorial plane, whilst in the following genus they are disposed over the whole surface of the disk. Stylotrochus corresponds to Astrocyclia among the Coccodiscida, to Stylodictya among the Porodiscida. The spongy framework of the disk is either quite irregular (Stylotrochiscus), or includes in the middle part some concentric circular rings (Stylospongia).

Subgenus 1. Stylotrochiscus, Haeckel.

Definition.—Spongy framework of the whole disk irregular, without concentric circular rings or spiral convolutions.

1. Stylotrochus arachnius, Haeckel.

Spongotrochus arachnius, Haeckel, 1862, Monogr. d. Radiol., p. 464.

Spongy framework of the whole disk irregular. Eight to twelve marginal spines very long and thin, bristle-shaped, twice to four times as long as the diameter of the disk. (Very similar to the common Stylodictya arachnia, but without concentric circular rings and sieve-plates, with quite irregular network of fine bars.)

Dimensions.—Diameter of the disk 0.12 to 0.15; length of the radial spines 0.2 to 0.6, basal breadth 0.001.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface; also fossil in Tertiary rocks of Barbados and the Mediterranean.

2. Stylotrochus craticulatus, Haeckel.

Spongotrochus craticulatus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 118, Taf. vi. fig. 12. ? Spongodiscus aculeatus, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 246.

Spongy framework of the whole disk irregular. Sixteen to twenty short marginal spines (twice to four times as long as the diameter of one mesh of the framework), free prolongations of internal radial beams which arise from the darker centre of the disk. (The interruption of the disk-margin on one point of its circumference, figured by Stöhr as osculum or "Mündungs-Oeffnung," is probably an accidental abnormality; I did not find it in other specimens.)

Dimensions.—Diameter of the disk 0.2 to 0.25; length of the radial spines 0.005 to 0.018, basal breadth 0.001 to 0.003.

Habitat.—Pacific, central area, Stations 266 to 268, surface; fossil in Barbados and Sicily.

3. Stylotrochus helianthus, n. sp.

Spongy framework of the whole disk irregular. Thirty to fifty very large, conical radial spines, about as long as the diameter of the disk, and at the base two to four times as broad as one mesh of the framework (without internal prolongations).

Dimensions.—Diameter of the disk 0.15 to 0.2; length of the radial spines 0.16 to 0.24, basal breadth 0.008 to 0.016.

Habitat.—Pacific, central area, Station 272, surface.

4. Stylotrochus rhabdostylus, Haeckel.

Spongosphæra rhabdostyla, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 256, Taf. xxvi. figs. 1, 2.

Spongy framework of the whole disk irregular. Four very large marginal primary spines crossed in two equatorial diameters, perpendicular one to another, and between them numerous (twelve to twenty or more) smaller secondary spines. The latter arise from the margin, whilst the former pierce the disk and are nearly united in its centre. All the spines are cylindrical, the smaller as broad as one mesh, the larger three to six times as broad.

Dimensions.—Diameter of the disk 0.2; length of the four main spines 0.15 to 0.3, breadth 0.01 to 0.02; length of the accessory spines 0.05 to 0.1, breadth 0.005.

Habitat.—Fossil in the rocks of Barbados.

5. Stylotrochus heteracanthus, Haeckel.

Spongotrochus heteracanthus, Haeckel, 1862, Monogr. d. Radiol., p. 464.

Spongy framework of the whole disk irregular. Ten very long needle-shaped marginal spines (symmetrically distributed), and between them numerous very fine, shorter, accessory, bristle-shaped spines.

Dimensions.—Diameter of the disk 0.16; length of the main spines 0.16, basal breadth 0.002; length of the secondary spines 0.03.

Habitat.—Mediterranean (Messina), surface.

Subgenus 2. Stylospongia, Haeckel, 1862, Monogr. d. Radiol., p. 473.

Definition.—Spongy framework of the disk in the inner part with concentric rings or spiral convolutions, in the outer part quite irregular.

6. Stylotrochus huxleyi, Haeckel.

Stylospongia huxleyi, Haeckel, 1862, Monogr. d. Radiol., p. 473, Taf. xxviii. fig. 7.

Spongy framework of the disk in the inner part with five concentric rings, in the outer part quite irregular. Ten marginal spines, conical at the base, about as long as the radius of the disk, without inner piercing prolongations.

Dimensions.—Diameter of the disk 0.12; length of the radial spines 0.06, basal breadth 0.003.

Habitat.—Mediterranean (Messina), Haeckel.

7. Stylotrochus geddesii, n. sp. (Pl. 41, fig. 11).

Stylospongidium geddesii, Haeckel, 1881, Atlas (pl. xli. fig. 11).

Spongy framework of the disk in the inner part with four to eight concentric rings (or partially spiral convolutions), in the outer part quite irregular. Thirty to fifty pyramidal marginal spines of variable size, one-fourth to one-half as long as the radius of the disk, outer prolongations of inner piercing radial beams, which arise from various concentric rings. I call this interesting species, which is intermediate between Stylodictya and Stylotrochus, in honour of the morphologist Mr. Patrick Geddes of Edinburgh.

Dimensions.—Diameter of the disk 0.15 to 0.25; length of the radial spines 0.03 to 0.06, basal breadth 0.004 to 0.01.

Habitat.—Pacific, central area, Stations 270 to 274, in 2350 to 2925 fathoms.

Genus 259. Spongotrochus,^[85] Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Definition.—Spongodiscida with numerous solid radial spines (five to ten or more), which are scattered over the whole surface and the margin of the disk, or regularly disposed on both sides of it.

The genus Spongotrochus differs from the foregoing and nearly allied genus by the distribution of the numerous radial spines. These are not confined to the margin of the disk, but also scattered on its whole surface, and sometimes symmetrically disposed on both its sides in a regular manner. Also in this genus the spongy framework is sometimes quite irregular (Spongotrochiscus), at other times in the middle part with enclosed concentric rings (Stylospongidium).

Subgenus 1. Spongotrochiscus, Haeckel, 1862, Monogr. d. Radiol., p. 463.

Definition.—Spongy framework of the whole disk irregular, without concentric rings or spiral convolutions.

1. Spongotrochus brevispinus, Haeckel.

Spongotrochus brevispinus, Haeckel, 1862, Monogr. d. Radiol., p. 462, Taf. xxvii. figs. 4, 5.

Spongy framework of the whole disk irregular, everywhere equal. The whole surface of the disk covered with numerous short, needle-shaped, radial spines, about as long as the thickness of the disk, which is one-fifth of its diameter.

Dimensions.—Diameter of the disk 0.18; length of the radial spines 0.03 to 0.04, basal breadth 0.002.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

2. Spongotrochus multispinus, n. sp.

Spongy framework of the whole disk irregular, in the centre darker. The whole surface of the disk covered with numerous conical radial spines, about as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.22; length of the radial spines 0.1, basal breadth 0.008.

Habitat.—Pacific, central area, Stations 271 to 274, surface.

3. Spongotrochus longispinus, Haeckel.

Spongotrochus longispinus, Haeckel, 1862, Monogr. d. Radiol., p. 463, Taf xxvii. figs. 2, 3.

Spongy framework of the whole disk irregular, everywhere equal. Surface thorny. Twenty long, needle-shaped, radial spines, about as long as the diameter of the disk, symmetrically distributed in pairs on both flat sides of the disk, so that the opposite pairs lie in five equidistant, meridian planes (compare the figures).

Dimensions.—Diameter of the disk 0.2; length of the twenty radial spines 0.2, basal breadth 0.001.

Habitat.—Mediterranean (Messina), surface.

Subgenus 2. Stylospongidium, Haeckel, 1881, Prodromus, p. 460.

Definition.—Spongy framework of the disk in the inner part with concentric rings or spiral convolutions, in the outer part quite irregular.

4. Spongotrochus scutella, n. sp.

Spongotrochus ehrenbergii, Bütschli, 1882, L. N. 41, Taf. xxvi. figs. 1a, 1b.

Spongy framework of the disk in the inner part with four to six concentric rings, in the outer part quite irregular. The whole surface of the disk covered with bristle-shaped radial spines, about half as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.24; length of the radial spines 0.06, basal breadth 0.02.

Habitat.—Antarctic Ocean, Station 157, depth 1950 fathoms.

5. Spongotrochus parma, n. sp.

Spongy framework of the disk in the inner part with five to eight spiral convolutions (or partly concentric rings), in the outer part quite irregular. Thirty to forty long, bristle-shaped, radial spines, about as long as the diameter of the disk, disposed on both flat sides of the disk, but not on the margin.

Dimensions.—Diameter of the disk 0.16; length of the radial spines 0.18, basal breadth 0.003.

Habitat.—South Atlantic, Station 325, surface.

Subfamily 3. Spongobrachida, Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with two or more (commonly three or four) spongy radial arms on the margin of the disk, situated in its equatorial plane (with or without a connecting patagium between the arms).

Genus 260. Spongolena,^[86] n. gen.

Definition.—Spongodiscida with two opposite spongy arms on the margin of the disk, without a connecting patagium.

The genus Spongolena opens the series of the Spongobrachida, or of the Spongodiscida provided with radial spongy arms on the margin of the disk. Spongolena is the most simple form of this subfamily, and bears only two simple opposite arms, without a connecting patagium. It corresponds to Amphibrachium (Porodiscida) and to Diplactura (Coccodiscida). Also there is no patagium. Spongolena may easily be confounded with Spongurus (compare my Prodromus, 1881, p. 461); but in the true Spongurus (an ellipsoid) the transverse section is circular, in Spongolena elliptical.

1. Spongolena rhopalura, n. sp.

Arms club-shaped, three times as long as broad, at the rounded distal end twice as broad as at the base, and twice as long as the diameter of the circular central disk. Surface nearly smooth.

Dimensions.—Radius of the arms (or the distance from the centre to the distal arm-end) 0.16, distal breadth 0.05, basal breadth 0.03.

Habitat.—Pacific, central area, Station 273, depth 2350 fathoms.

2. Spongolena spongura, n. sp.

Arms nearly cylindrical, twice as long as broad, and a little longer than the diameter of the elliptical central disk. Surface thorny, some longer bristle-shaped spines on the distal end of the arms. (Very similar to the ellipsoid Spongurus cylindricus, Monogr. d. Radiol., p. 465, Taf. xxvii. fig. 1, but differs in the compressed lenticular (not ellipsoidal) form of the central disk; the transverse section of the arm is elliptical, not circular.)

Dimensions.—Radius of the arms 0.1, breadth 0.04.

Habitat.—Pacific, central area, Station 270, depth 2925 fathoms.

3. Spongolena cypselura, n. sp.

Arms nearly triangular, not longer than broad, about half as large as the elliptical central disk, at the broader distal end with two very large, widely divergent lateral spines, and between them several smaller, like the tail of a swallow. Surface thorny.

Dimensions.—Radius of the arms 0.2, distal breadth (without spines) 0.15, basal breadth 0.07.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

Genus 261. Spongobrachium,^[87] Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with two opposite spongy arms on the margin of the disk, connected by a spongy patagium of different texture.

The genus Spongobrachium differs from the foregoing only in the loose spongy patagium, which envelops both opposite spongy arms. It corresponds to Amphymenium among the Porodiscida and to Amphiactura among the Coccodiscida.

1. Spongobrachium ellipticum, Haeckel.

Spongocyclia elliptica, Haeckel, 1862, Monogr. d. Radiol., p. 470, Taf. xxviii. fig. 2. Spongodiscus ellipticus, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Arms nearly square, scarcely as long and broad as the radius of the circular central disk, at the broader distal end truncated. Patagium complete, enveloping the whole disk with the arms, and forming a larger elliptical disk of looser framework. (In my Monograph, 1862, loc. cit., I had not distinguished the opposite darker arms, opposite in the longer axis of the elliptical disk, from the enveloping looser framework of the patagium. In larger specimens of the Challenger collection this distinction is very evident.)

Dimensions.—Radius of the arms 0.12, breadth 0.05; major axis of the elliptical patagium 0.24, minor 0.16.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

2. Spongobrachium lanceolatum, n. sp.

Arms club-shaped, twice as long as broad, at the distal end pointed, five times as long as the radius of the circular central disk. Patagium complete, enveloping the whole disk with the arms, and forming a larger lanceolate disk of looser framework. (Similar in form to Amphymenium pupula, Pl. 44, fig. 8, but with an irregular spongy framework and pointed ends.)

Dimensions.—Radius of the arms 0.16, breadth 0.05; major axis of the lanceolate patagium 0.32, minor axis 0.12.

Habitat.—Pacific, central area, Station 270, surface.

Genus 262. Rhopalodictyum,^[88] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 830.

Definition.—Spongodiscida with three spongy arms on the margin of the circular or triangular disk, without a connecting patagium.

The genus Rhopalodictyum comprises those very common forms of Spongodiscida in which the margin of the disk is provided with three simple, free, spongy arms. It corresponds to Dictyastrum and Rhopalastrum among the Porodiscida, to Trigonactura among the Coccodiscida. The typical species of this genus is Rhopalodictyum abyssorum of Ehrenberg, the only species figured by him. His diagnosis of the genus was very insufficient, and agreed with that of his Dictyastrum (compare above the improved diagnosis of this genus, p. 526, and my Monograph, p. 466).

Subgenus 1. Rhopalodictya, Haeckel.

Definition.—Triangular shell regular, with three arms of equal size and equidistant.

1. Rhopalodictyum abyssorum, Ehrenberg.

Rhopalodictyum abyssorum, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. viii. fig. 17.

Arms of equal size and equidistant, club-shaped, about as long as the diameter of the triangular central disk, and a little longer than the breadth of the pear-shaped rounded distal end. Surface rough.

Dimensions.—Radius of the arms 0.11, basal breadth 0.03, distal breadth 0.06.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific; tropical zone, surface.

2. Rhopalodictyum truncatum, Ehrenberg.

Rhopalodictyum truncatum, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 301. ? Dictyastrum angulatum, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 289, Taf. viii. fig. 18.

Arms of equal size and equidistant, nearly square, with straight edges, towards the truncated end a little broader, about of the same diameter as the central triangular disk. This species is indicated by Ehrenberg only by the short diagnosis, "Radiis stellæ tribus apice truncatis." It is probably identical with his figure of Dictyastrum angulatum (loc. cit.). This latter name I have retained for the similar Porodiscid (above, p. 526), mainly because the genera Dictyastrum and Rhopalodictyum, according to the insufficient diagnosis of Ehrenberg, seem to be identical. (Compare my Monograph, 1862, p. 466.)

Dimensions.—Radius of each arm 0.13, basal breadth 0.09, distal breadth 0.1.

Habitat.—Tropical Pacific, Philippine Sea, Station 200, depth 250 fathoms; Atlantic (Mexican Gulf Stream).

3. Rhopalodictyum subacutum, Ehrenberg.

Rhopalodictyum subacutum, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 301.

Arms of equal size and equidistant, club-shaped, three times as long as the diameter of the central disk, which equals the breadth of the thickened distal end; the latter is armed with a strong pyramidal terminal spine. (The diagnosis of Ehrenberg is "Radiis stellæ tribus, apice cuneatis subacutis.")

Dimensions.—Radius of the arms 0.2, basal breadth 0.04, distal breadth 0.07.

Habitat.—North Atlantic, surface and various depths; Greenland; Mexican Gulf Stream; Færöe Channel (John Murray).

4. Rhopalodictyum bifidum, n. sp.

Arms of equal size and equidistant, in the distal half forked, twice as long as the diameter of the central disk; both fork branches half as broad as the simple basal part, truncated at the distal end.

Dimensions.—Radius of the arms 0.16, basal breadth 0.08, distal breadth 0.04.

Habitat.—North Pacific, Station 237, surface.

Subgenus 2. Triactinosphæra, Dunikowski, 1882, Denkschr. d. k. Akad. d.

Wiss. Wien, vol. 45, ii. p. 192.

Definition.—Triangular shell bilateral or irregular, with three arms of different size or distance.

5. Rhopalodictyum zittelii, Haeckel.

Triactinosphæra zittelii, Dunikowski, 1882, Denkschr. d. k. Akad. d. Wiss, Wien, vol. 45, ii. p. 192.

Arms of different size and at unequal distances, one odd arm being a little shorter than the two paired arms; the odd angle between the latter is larger than the paired angles between them and the former. Arms club-shaped, their basal semi-cylindrical, half as broad as the spherical distal half, which bears a strong, conical, terminal spine. The discoverer of this remarkable, very old, Liassic species, Dunikowski, supposes that it is not a true Discoid, from the absence of a central disk; in my opinion the central disk (nearly spherical) has the same relation to the arms as in many other Discoidea, their equatorial plane is the same.

Dimensions.—Radius of the odd arm 0.18, of the paired arms 0.24; basal breadth 0.08, distal breadth 0.16.

Habitat.—Fossil in the Alpine Lias, Schafberg, near Salzburg, Dunikowski.

6. Rhopalodictyum elongatum, n. sp.

Arms of different size and at unequal distances, one odd arm being twice as long as both paired arms; the odd angle between the latter much larger than both equal paired angles. Arms nearly cylindrical, little flattened, three to six times as long as broad, with rounded blunt distal end.

Dimensions.—Radius of the arms 0.15 to 0.3, breadth 0.05.

Habitat.—Pacific, central area, Station 274, surface.

7. Rhopalodictyum curvatum, n. sp.

Arms of different size and at unequal distances, irregular, more or less curved, nearly cylindrical, five to ten times as long as broad, with rounded blunt distal end. (There were observed only two specimens of this remarkable irregular species; in one specimen all three arms were simple, in the other one odd arm forked. The length of the arms and the size of the angles between them seems to be very different and variable.)

Dimensions.—Radius of the arms 0.3 to 0.6 to 1.15, breadth 0.06 to 0.12.

Habitat.—Pacific, central area, Station 271, surface.

Genus 263. Dictyocoryne,^[89] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 830.

Definition.—Spongodiscida with three spongy arms on the margin of the circular or triangular disk, connected by a spongy patagium of different texture.

The genus Dictyocoryne differs from the foregoing Rhopalodictyum only in the patagium, connecting the three spongy arms, and bears to it the same relation as in the Porodiscida Euchitonia does to Rhopalastrum. The typical species of this genus is Dictyocoryne profunda, the only species figured by Ehrenberg. After his insufficient diagnosis Dictyocoryne was identical with his Spongaster (compare my Monograph, p. 467); but as the type of this latter genus (Spongaster tetras) figured by him, 1872, had four crossed arms, we retain this genus here separate.

Subgenus 1. Dictyocorynula, Haeckel.

Definition.—Triangular shell regular, with three arms of equal size and equal distance.

1. Dictyocoryne profunda, Ehrenberg.

Dictyocoryne profunda, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 307, Taf. vii. fig. 23.

Arms of equal size and equidistant, club-shaped, in the outer circular half three times as broad as in the inner cylindrical half, and much larger than the small triangular central disk. Patagium complete, forming an equilateral triangle with rounded corners.

Dimensions.—Radius of the arms 0.14, basal breadth 0.025, distal breadth 0.07.

Habitat.—Pacific, Philippine Sea, depth 3300 fathoms, Ehrenberg; Station 198, depth 2150 fathoms; Station 274, depth 2750 fathoms.

2. Dictyocoryne tetradiscus, n. sp.

Arms of equal size and equidistant, club-shaped, their outer circular half is quite as large as the circular central disk, and is connected with it by the thin cylindrical inner half, which is scarcely one-fourth as broad. Patagium complete, forming an equilateral triangle with rounded corners and convex sides.

Dimensions.—Radius of the arms 0.16, basal breadth 0.02, distal breadth 0.08.

Habitat.—Pacific, central area, Stations 271 to 274, in 2350 to 2750 fathoms.

3. Dictyocoryne euchitonia, Haeckel.

Dictyocoryne euchitonia, Haeckel, 1862, Monogr. d. Radiol., p. 468.

Arms of equal size and equidistant, lanceolate, twice as long as broad in the distal part, and three times as long as the small circular central disk. Patagium complete, forming an equilateral triangle with pointed corners. (Very similar to Euchitonia köllikeri, Monograph, 1862, p. 511, Taf. xxxi. fig. 6, but quite spongy, not concentric.)

Dimensions.—Radius of the arms 0.15, basal breadth 0.03, distal breadth 0.06.

Habitat.—Mediterranean (Messina), Haeckel.

4. Dictyocoryne trigona, n. sp.

Arms of equal size and equidistant, lanceolate, three times as long as broad in the middle part, and as the diameter of the triangular central disk; their distal end armed with a strong conical radial spine. Patagium complete, forming an equilateral triangle with pointed corners.

Dimensions.—Radius of the arms 0.2, basal breadth 0.02, distal breadth 0.06.

Habitat.—North Atlantic, Canary Islands, surface.

Subgenus 2. Dictyocorynium, Haeckel.

Definition.—Triangular shell bilateral or irregular, with three arms of different sizes or at different distances.

5. Dictyocoryne charybdaea, Haeckel.

Spongocyclia charybdaea, Haeckel, 1862, Monogr. d. Radiol., p. 472, Taf. xxviii. figs. 5, 6. Spongodiscus charybdaeus, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Arms at different distances, nearly equilateral triangular, scarcely half as long as the radius of the large circular central disk. Both paired arms touching at their bases, separated by a great distance from the opposite odd arm. Patagium complete, nearly pentagonal. (The illustration in my Monograph, in the coloured plate xxviii., is better than my description, as I had not exactly separated the arms from the patagium.)

Dimensions.—Radius of the arms 0.18, basal breadth 0.08.

Habitat.—Mediterranean (Messina), surface.

6. Dictyocoryne pentagona, Stöhr.

Dictyocoryne pentagona, Stöhr, 1880, Palæontogr., vol. xxvi. p. 118, Taf. vii. fig. 2.

Arms at different distances, club-shaped, little longer than broad at their rounded distal end. Both paired arms smaller and more approximate than the opposite odd arm. Patagium complete, very large, enveloping the whole shell, and forming a pentagon with rectilinear base and transverse constriction, and with five rounded corners.

Dimensions.—Radius of the arms 0.1 to 0.15, middle breadth 0.04.

Habitat.—Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.

7. Dictyocoryne agrigentina, Stöhr.

Dictyocoryne agrigentina, Stöhr, 1880, Palæontogr., vol. xxvi. p. 118, Taf. vii. fig. 1.

Arms at different distances, club-shaped, about twice as long as broad, and smaller than the large triangular central disk. Both paired arms smaller and more approximate than the opposite odd arm. Patagium incomplete, enveloping only the basal half of the arms as a circular spongy disk of loose framework.

Dimensions.—Radius of the arms 0.18, basal breadth 0.05, distal breadth 0.08.

Habitat.—Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.

8. Dictyocoryne echinata, n. sp.

Arms unequal and at different distances, club-shaped, in the distal half twice as broad as in the basal half, three times as long as the small triangular central disk, at their distal end armed with one larger and several smaller conical spines. Both paired arms with touching bases, and only half as large as the doubly remote odd arm. Patagium incomplete, enveloping only the basal half of the arms, and forming a circular disk of looser framework. Surface thorny.

Dimensions.—Radius of the arms 0.15 to 0.2, basal breadth 0.03, distal breadth 0.06.

Habitat.—South Atlantic, Station 325, surface.

Genus 264. Spongasteriscus,^[90] Haeckel, 1862, Monogr. d. Radiol., p. 474 (sensu restricto).

Definition.—Spongodiscida with four spongy arms on the margin of the circular or quadrangular disk, crossed in two equatorial diameters, without a connecting patagium.

The genus Spongasteriscus (in the restricted definition here stated) exhibits on the margin of the disk four spongy arms, which form either a regular or a bilateral cross. It corresponds to Stauralastrum and Myelastrum among the Porodiscida, to Astractura among the Coccodiscida.

Subgenus 1. Spongasteriscinus, Haeckel.

Definition.—Cross formed by the four arms regular, rectangular, with equal-sized and equidistant arms.

1. Spongasteriscus ovatus, n. sp.

Arms at equal distances, forming a regular, rectangular cross, egg-shaped, with a broader rounded distal end, one and a third times as long as broad, and three times as long as the radius of the central disk; in the latter three to four concentric rings.

Dimensions.—Radius of the arms 0.1, greatest breadth 0.06.

Habitat.—Western Tropical Pacific, Station 225.

2. Spongasteriscus clavatus, n. sp.

Arms at equal distances, forming a regular, rectangular cross, club-shaped, about as long as the diameter of the central disk, and at their rounded distal end one and a third times as long as broad, at their narrow base only one third as broad. In the centre five to six concentric rings.

Dimensions.—Radius of the arms 0.13, distal breadth 0.06, basal breadth 0.02.

Habitat.—Pacific, central area. Station 271, surface.

3. Spongasteriscus mucronatus, n. sp.

Arms at equal distances, forming a regular, rectangular cross, club-shaped, three times as long as the radius of the central disk, in the distal half nearly circular, three to four times as broad as at the narrow base. The rounded distal end armed with a strong pyramidal spine. In the centre no concentric rings. (Similar to Stauralastrum rhopalophorum, Pl. 45, fig. 1, but quite spongy.)

Dimensions.—Radius of the arms 0.12, basal breadth 0.03, distal breadth 0.02.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

4. Spongasteriscus furcatus, n. sp.

Arms at equal distances, forming a regular, rectangular cross, in the distal third forked; both fork branches half as long as the basal undivided part of the arm, which is twice as long as broad. Distal ends of the eight branches blunt, rounded. In the central disk no concentric rings.

Dimensions.—Radius of the arms 0.12, basal breadth 0.03; distal breadth of the branches 0.02.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

5. Spongasteriscus armatus, n. sp.

Arms at equal distances, forming a rectangular, regular cross, in the distal half forked; both fork branches of the same length as the basal undivided part of the arm, which is nearly square. Distal ends of the eight branches armed with a strong pyramidal spine. In the central disk no concentric rings. (Similar to Dicranastrum cornutum, Pl. 45, fig. 2, but quite spongy.)

Dimensions.—Radius of the arms 0.18, basal breadth 0.03, distal breadth 0.015.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

Subgenus 2. Spongasterisculus, Haeckel.

Definition.—Cross formed by the four arms, bilateral or irregular, with the arms at different distances.

6. Spongasteriscus quadricornis, Haeckel.

Spongasteriscus quadricornis, Haeckel, 1862, Monogr. d. Radiol., p. 474, Taf. xxviii. figs. 8-10. Spongodiscus quadricornis, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Arms at different distances, forming a bilateral or irregular cross, grouped in two opposite pairs; their form equilateral triangular; their length smaller than the radius of the large circular central disk, which exhibits in the interior eight to sixteen concentric rings.

Dimensions.—Radius of the arms 0.2, of the central disk 0.13; basal breadth of the arms 0.08.

Habitat.—Mediterranean (Messina), Haeckel, surface.

7. Spongasteriscus tetraceros, Haeckel.

Spongasteriscus tetraceros, Haeckel, 1862, Monogr. d. Radiol., p. 475.

Arms at different distances, forming a bilateral or irregular cross, grouped in two opposite pairs; their form isosceles triangular; their length larger than the radius of the large elliptical central disk, which exhibits in the interior six to twelve concentric rings.

Dimensions.—Radius of the arms 0.16, of the central disk 0.1; basal breadth of the arms 0.06.

Habitat.—Mediterranean (Messina), North Atlantic (Canary Islands), surface.

8. Spongasteriscus myelastrum, n. sp.

Arms at different distances, forming a bilateral or irregular cross, grouped in two opposite pairs; the arms of one pair broader and shorter than the arms of the other pair. Each arm in its basal half simple, in the distal half forked; ends of the fork branches blunt. In the central disk no concentric rings. (Similar to Myelastrum octocorne, Pl. 47, fig. 12, but quite spongy.)

Dimensions.—Radius of the arms 0.2, basal breadth 0.05, distal breadth 0.02.

Habitat.—North Pacific, Station 236, surface.

Genus 265. Spongaster,^[91] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 833.

Definition.—Spongodiscida with four spongy arms on the margin of the circular or quadrangular disk, connected by a spongy patagium of different texture.

The genus Spongaster differs from the foregoing Spongasteriscus in the patagium connecting the spongy arms, and bears therefore to it the same relation as, in the Porodiscida, Histiastrum does to Stauralastrum, or, in the Coccodiscida, Stauractura does to Astractura. The typical specimen, figured by Ehrenberg (Spongaster tetras), exhibits a regular, square disk, as also some other species. In a certain number of other species (formerly united by me with Spongocyclia) the quadrangular disk is bilateral.

Subgenus 1. Spongastrella, Haeckel.

Definition.—Cross formed by the four arms regular, rectangular, with the arms of equal size and equidistant.

1. Spongaster tetras, Ehrenberg.

Spongaster tetras, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. vi. (iii.) fig. 8. Dictyocoryne tetras, Haeckel, 1862, Monogr. d. Radiol., p. 469.

Arms at equal distances, forming a rectangular, regular Myelastrum, papiliocross, club-shaped, about twice as long as the diameter of the square central disk and eight times as long as broad at their base. Distal ends rounded, perfectly enclosed by the complete patagium, which forms a regular square, with slightly concave sides.

Dimensions.—Radius of the arms 0.12, distal breadth 0.03, basal breadth 0.015; length of the square side 0.2.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, surface and in various depths.

2. Spongaster quadratus, n. sp.

Arms at equal distances, forming a regular, rectangular cross, club-shaped, about four times as long as the diameter of the central circular disk, and five times as long as broad at the base. Basal third of the arms square; distal two thirds triangular, three times as broad, with a truncated distal end. Patagium complete, perfectly enveloping the arms, and bordered by an elegant, radially striated, broad edge, forming a regular square. (Similar to Histiastrum quadratum, Pl. 46, fig. 4, but quite spongy.)

Dimensions.—Radius of the arms 0.15, distal breadth 0.06, basal breadth 0.02; length of the square side 0.25.

Habitat.—Pacific, central area, Stations 270 to 274, depths 2350 to 2925 fathoms.

3. Spongaster cruciatus, n. sp.

Arms at equal distances, forming a rectangular, regular cross, lanceolate, three times as long as broad and as the diameter of the central circular disk. Ends of the arms provided with a short conical spine. Patagium incomplete, enveloping only the basal half of the arms, forming a regular square with concave sides.

Dimensions.—Radius of the arms 0.18, greatest breadth 0.05; length of the square side 0.2.

Habitat.—South Pacific, Station 288, surface.

4. Spongaster pentacyclus, n. sp.

Arms at equal distances, forming a rectangular, regular cross, of the same size and form as the circular central disk, so that the dark interior part of the shell is composed of five equal circular disks, situated in a quincuncial manner. The clearer complete patagium, enveloping the whole cross perfectly, forms a regular square with rounded edges.

Dimensions.—Radius of the arms 0.2; diameter of each of the five circular disks 0.01; length of the square side 0.35.

Habitat.—West Indies, Cuba, surface (Thomson).

Subgenus 2. Spongastromma, Haeckel.

Definition.—Cross formed by the four arms bilateral or irregular, with the arms at different distances.

5. Spongaster orthogonus, Haeckel.

Spongocyclia orthogona, Haeckel, 1862, Monogr. d. Radiol., p. 471, Taf. xxviii. fig. 3. Spongodiscus orthogonus, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Arms at different distances, forming a bilateral cross, grouped in two opposite pairs of equal size and similar form. Arms club-shaped, about as long as the diameter of the central circular disk, enveloped perfectly by the complete patagium, which forms a regular rectangle, the longer side of which is one and a half times as long as the shorter side. (The arms in my figure are not distinctly enough marked.)

Dimensions.—Radius of the arms 0.08, breadth 0.02; length of the larger side of the rectangle 0.15, of the smaller 0.1.

Habitat.—Mediterranean (Messina), surface.

6. Spongaster scyllaeus, Haeckel.

Spongocyclia scyllaea, Haeckel, 1862, Monogr. d. Radiol., p. 471, Taf. xxviii. fig. 4. Spongodiscus scyllaeus, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Arms at different distances, forming a bilateral cross, grouped in two opposite pairs of different size and form, one pair smaller and less divergent than the other. Arms club-shaped, little longer than the radius of the central circular disk, enveloped perfectly by the complete patagium, which forms a trapezium; the convergent longer sides of the latter are one and a half times as long as the larger, and twice as long as the smaller parallel side. (The arms are in my figure, loc. cit., not distinctly enough marked.)

Dimensions.—Radius of the arms 0.12 to 0.14, breadth 0.02; length of both convergent sides 0.24, of the larger parallel side 0.18, of the smaller 0.12.

Habitat.—Pacific, central area, Station 272, surface; Mediterranean (Messina).

1. Cenodiscus = Hollow disk; κενός, δίσκος.
2. Zonodiscus = Disk with girdle; ζώνη, δίσκος.
3. Stylodiscus = Disk with styles; στῦλος, δίσκος.
4. Theodiscus = Divine disk; θεός, δίσκος.
5. Crucidiscus = Disk with cross.
6. Trochodiscus = Wheel-disk; τροχός, δίσκος.
7. Sethodiscus = Sieve-disk; σηθός, δίσκος.
8. Phacodiscus = Lenticular disk; φακός, δίσκος.
9. Periphæna = Shell with transparent girdle; περιφαῖνα.
10. Perizona = Shell with surrounding girdle; περί, ζώνη.
11. Sethostylus = Sieve with styles; σηθός, στῦλος.
12. Phacostylus = Lens with styles; φακός, στῦλος.
13. Triactiscus = Shell with three rays; τριακτίσκος.
14. Sethostaurus = Sieve-cross; σηθός, σταυρός.
15. Phacostaurus = Lens with cross; φακός, σταυρός.
16. Distriactis = Shell with twice three rays; διστριακτίς.
17. Heliosestrum = Sun-sieve; ἥλιος, σῆστρον.
18. Astrosestrum = Stellated sieve; ἄστρον, σῆστρον.
19. Heliodiscus = Sun-disk; ἥλιος, δίσκος.
20. Heliodrymus = Sun-forest; ἥλιος, δρῦμος.
21. Astrophacus = Star-lens; ἄστρον, φακός.
22. Lithocyclia = Circular stone; λίθος, κύκλιον.
23. Coccodiscus = Disk with nucleus; κόκκος, δίσκος.
24. Stylocyclia = Circular shell with styles; στῦλος, κύκλιον.
25. Amphicyclia = Circular shell with spines on both sides; ἀμφί, κύκλιον.
26. Trigonocyclia = Triangular shell with circular rings; τρίγονον, κύκλιον.
27. Staurocyclia = Circular shell with four crossed spines; σταυρός, κύκλια.
28. Astrocyclia = Stellated circular shell; ἄστρον, κύκλιον.
29. Coccocyclia = Circular shell with nucleus; κόκκος, κύκλιος.
30. Diplactura = Stellated shell with double tail; δίπλους, ἀκτίς, ὀυρά.
31. Amphiactura = Stellated shell with tail on both sides; ἀμφί, ἀκτίς, ὀυρά.
32. Trigonactura = Triangular shell with three rays; τρίγονον, ἀκτίς, ὀυρά.
33. Hymenactura = Star-shaped shell with membrane between the rays; ὑμήν, ἀκτίς, ὀυρά.
34. Astractura = Star-shaped shell with many rays; ἄστρον, ἀκτίς, ὀυρά.
35. Stauractura = Cruciform shell with four rays; σταυρός, ἀκτίς, ὀυρά.
36. Pentactura = Stellated shell with five rays; πέντε, ἀκτίς, ὀυρά.
37. Echinactura = Echinus-like shell with five rays; ἐχῖνος, ἀκτίς, ὀυρά.
38. Archidiscus = Primordial disk; ἀρχιδισκος.
39. Axodiscus = Disk with certain axes; ἄξις, δίσκος.
40. Porodiscus = Porous disk; πόρος, δίσκος.
41. Perichlamydium = Shell surrounded by a mantle; περί, χλαμύδιον.
42. Ommatodiscus = Disk with eyes; ὄμμα, δίσκος.
43. Stomatodiscus = Disk with openings; στόμα, δίσκος.
44. Xiphodictya = Net with swords; ξίφος, δίκτυον.
45. Tripodictya = Net with tripod; τρίπους, δίκτυον.
46. Staurodictya = Cross-net; σταυρός, δίκτυον.
47. Stylodictya = Net with styles; στῦλος, δίκτυον.
48. Stylochlamydium = Shell with styles and mantle; στῦλος, χλαμύδιον.
49. Amphibrachium = Shell with two arms; ἀμφί, βραχίων.
50. Amphymenium = Shell with veil on both sides; ἀμφί, ὑμήνιον.
51. Amphirrhopalum = Shell with clubs on both sides; ἀμφί, ῥόπαλον.
52. Amphicraspedum = Shell with borders on both sides; ἀμφί, κράσπεδον.
53. Dictyastrum = Reticulated star; δίκτυον, ἄστρον.
54. Rhopalastrum = Club-star; ῥόπαλον, ἄστρον.
55. Hymeniastrum = Membranous star; ὑμήν, ἄστρον.
56. Euchitonia = Nice shell; εὖ, χιτωνία.
57. Chitonastrum = Star-shell; χιτωνία, ἄστρον.
58. Trigonastrum = Triangular star; τρίγωνον, ἄστρον.
59. Stauralastrum = Crossed sea-star; σταυρός, ἅλς, ἄστρον.
60. Hagiastrum = Holy starrulet; ἅγιον, ἄστρον.
61. Histiastrum = Star with enveloping tissue; ἱστιόν, ἄστρον.
62. Tessarastrum = Starrulet with four rays; τέσσαρα, ἄστρον.
63. Stephanastrum = Garland-starrulet; στέφανος, ἄστρον.
64. Dicranastrum = Fork-starrulet; δίκρανον, ἄστρον.
65. Myelastrum = Medullary starrulet; μύελος, ἄστρον.
66. Pentalastrum = Little sea-star with five rays; πέντε, ἅλς, ἄστρον.
67. Pentinastrum = Starrulet with five rays; πέντε, ἴνος, ἄστρον.
68. Pentophiastrum = Starrulet with five snakes; πέντε, ὄφις, ἄστρον.
69. Hexalastrum = Little sea-star with six rays; ἕξα, ἅλς, ἄστρον.
70. Hexinastrum = Starrulet with six rays; ἕξα, ἴνος, ἄστρον.
71. Triolena = Shell with three arms; τρία, ὠλένη.
72. Triopyle = With three gate-openings; τρία, πύλη.
73. Triodiscus = Disk with three openings; τριοδίσκος.
74. Pylolena = Disk with alternating gates and arms; πύλη, ὠλένη.
75. Hexapyle = With six gate-openings; ἕξα, πύλη.
76. Pylodiscus = Disk with gates; πύλη, δίσκος.
77. Discozonium = Disk with girdle; δίσκος, ζωνίον.
78. Discopyle = Disk with gate; δίσκος, πύλη.
79. Spongodiscus = Spongy disk; σπόγγος, δίσκος.
80. Spongophacus = Spongy lens; σπόγγος, φάκος.
81. Spongolonche = Spongy disk with spontoons; σπόγγος, λόγχη.
82. Spongotripus = Spongy disk with tripod; σπόγγος, τρίπους.
83. Spongostaurus = Spongy disk with crossed spines; σπόγγος, σταυρός.
84. Stylotrochus = Wheel with styles; στῦλος, τροχός.
85. Spongotrochus = Spongy wheel; σπόγγος, τρόχος.
86. Spongolena = Spongy disk with two arms; σπόγγος, ὠλένη.
87. Spongobrachium = Spongy shell with two arms; σπόγγος, βραχίων.
88. Rhopalodictyum = Network with clubs; ῥόπαλον, δίκτυον.
89. Dictyocoryne = Net with clubs; δίκτυον, κορύνη.
90. Spongasteriscus = Spongy star; σπόγγος, ἀστερίσκος.
91. Spongaster = Spongy star; σπόγγος, ἀστήρ.