Report on the Radiolaria/Stephoidea

by Ernst Haeckel

Suborder III. STEPHOIDEA, Haeckel.

Stephoidea vel Stephida, Haeckel, 1881, Prodromus, p. 444.
Acanthodesmida (sensu ampliori), Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 495.

Definition.—Nassellaria without complete lattice-shell, with a skeleton composed of one or more simple rings, which may be united by a loose framework and are separated by large openings or gates. One primary or sagittal ring, determining the sagittal or median plane of the bilateral body, encloses the monaxonian central capsule.

The suborder Stephoidea, hitherto known by a few species only of "Acanthodesmida," comprises a large number of interesting Nassellaria (now more than two hundred species), which possess peculiar interest for the morphology and phylogeny of this legion. The monaxonian central capsule of the Stephoidea is surrounded either by one simple ring or by a complex system of several loosely connected rings; these may be united by a loose framework of connected branches, but never produce a complete lattice-shell, as is constantly the case in the Spyroidea, Botryodea, and Cyrtoidea. Therefore there remain between the parts of the connected rings a few large openings which we call "gates," separating them from the numerous small "pores" of the complete lattice-shells. In the most simple case, if only one ring be formed, there is also present only one "gate," the aperture of this simple ring.

The first known species of Stephoidea were observed in the Mediterranean by Johannes Müller in 1856, and described and figured in his last treatise (1858) under the names Lithocircus annularis (loc. cit., Taf. i. fig. 1) and Acanthodesmia vinculata (loc. cit., Taf. i. figs. 4-7). In the following year I myself observed two other living species in the Mediterranean, and described them in my Monograph (1862, pp. 268, 270) as Zygostephanus mülleri (Taf. xii. fig. 2) and Prismatium tripleurum (Taf. iv. fig. 6). For these four longest known Stephoidea I founded the new family of Acanthodesmida (loc. cit., p. 265), but united with them two other similar genera which I afterwards separated:—Plagiacantha (belonging to the Plectoidea) and Dictyocha (belonging to the Phæodaria).

When, in 1876, I received the rich material of the Challenger collection, I was astonished to find in it an enormous number of new, similar, and partly very interesting "Acanthodesmida," which were afterwards arranged in my Prodromus (1881, p. 444) in thirty-eight different genera and four "subfamilies," all united in one single large family, "Stephida or Monopylaria cricoidea." I retain here this natural group in the same sense, but give to it the rank of a "suborder," separating at the same time its four subfamilies as substantial "families." Since the names of the latter, proposed in the Prodromus, were not quite suitable, I replace them here by the following more convenient names:—

1. Family Stephanida (= Monostephida, 1881, p. 447). Skeleton entirely formed by one simple ring (the primary vertical sagittal ring). The only "gate" is the simple aperture of the ring.

2. Family Semantida (= Dyostephida, 1881, p. 446). Skeleton composed of two rings, perpendicular to one another; the primary vertical sagittal ring bears at the base a horizontal basal ring; between the two rings two or more "basal gates remain."

3. Family Coronida (= Triostephida, 1881, p. 445). Skeleton composed of two crossed vertical or meridional rings, perpendicular to one another—the primary sagittal ring and the secondary frontal ring. Commonly the two vertical rings are united at the base by a horizontal basal ring, and between them remain two or more "basal gates."

4. Family Tympanida (= Parastephida, 1881, p. 446). Skeleton composed of two parallel horizontal rings, and upper mitral ring, and a lower basal ring, both connected by vertical or divergent columellæ, which are parts of vertical rings (primary sagittal, and secondary frontal ring).

The peculiar structure of the central capsule of the Stephoidea, and their character as true Monopylea, were first recognised by Richard Hertwig, who in 1879, in his Organismus der Radiolarien, gave an excellent detailed description of it (loc. cit., pp. 68-72, Taf. vii. figs. 4, 5). He also pointed out the near affinity of these "Acanthodesmida" with the Spyroidea or Zygocyrtida, uniting the latter with the former family.

A fuller explanation of this affinity, and of the morphological and phylogenetic importance of the "Acanthodesmida," as ancestral forms of the Spyroidea and Cyrtoidea, was given in 1882 by Bütschli (Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 495-501). He described in detail some important fossil forms of Acanthodesmida as different species of "Stephanolithis," a name which Ehrenberg had employed for various ring-like fragments of Radiolarian shells, sponges, and other fossil bodies. The four fossil species which Bütschli described represent four different genera of Stephoidea, viz., Semantis (spinescens), Semantrum (mülleri), Semantidium (haeckelii), and Tristephanium (hertwigii). On the phylogenetic conclusions, derived from these accurate observations, compare above, p. 893, &c. The topographical signification of the parts, employed by Bütschli, is contrary to mine; he calls my dorsal side the "anterior," and my ventral side the "posterior."

The geometrical fundamental form of the body in nearly all Stephoidea (with few exceptions) is distinctly bilateral or "dipleuric," so that we can easily distinguish the three different dimensive axes: the principal axis with different apical and basal poles, the sagittal axis with different dorsal and ventral poles, and the lateral axis with equivalent right and left poles. In only a few genera this bilateral symmetry is not expressed, and a simpler, more regular fundamental form appears. The latter may be either primary (in the monaxonian Archicircus and Lithocircus) or secondary, afterwards acquired (in the octahedral Trissocircus and Trissocyclus, the cubical Lithocubus, the prismatic Eutympanium, and some other forms).

The most important element of the skeleton, with which the formation begins, in all Stephoidea is the simple primary or sagittal ring, lying vertically in the sagittal or median plane of the body and surrounding the monaxonian central capsule. This sagittal ring is the only essential element of the skeleton in all Stephanida, and is completely preserved in all Semantida, also in the greater part of the Coronida and Tympanida. It is partially reduced in the small groups of the true Acanthodesmida (subfamily of Coronida) and the Dystympanida and Eutympanida (subfamilies of Tympanida). Here only the vertical parts of it are preserved (dorsal and ventral rod), whilst the horizontal parts are lost (mitral and basal rod).

The sagittal ring lies constantly in the vertical median plane of the body, and therefore divides the enclosed central capsule into a right and a left half. It is rarely regular or subregular, commonly dipleuric or distinctly bilateral, so that we may easily distinguish its dorsal and ventral, apical and basal parts. The most important of these four parts or "rods" is the "basal rod" or the inferior part, because here the ring is in closer connection with the central capsule and its "porous area"; here peculiar spines or branches are commonly developed, which even on the isolated ring immediately determine the basal pole. The opposite upper part, or the "mitral rod," is also often distinguished by the peculiar appendages. The posterior part, or the "dorsal rod" (the anterior rod, a, in the description of Bütschli), is commonly more straight, often quite vertical. The opposite anterior part, or the "ventral rod" (the posterior rod, b, of Bütschli), is usually more convex, and often strongly curved or semicircular.

Whilst this dipleuric or bilateral (commonly obliquely ovate or nearly triangular) form of the sagittal ring is distinctly preserved in by far the greater number of Stephoidea, it is replaced in some few genera by a more regular, amphithect, diphragmatic, or biradial form. In this case we may often suppose a primary regularity to exist, the dorsal and ventral parts being not yet differentiated, as in Archicircus and Lithocircus, Zygostephanus and Protympanium, and perhaps also in some other forms. But in other cases the regularity is, on the contrary, secondary, being derived from original bilateral forms.

The rod of the sagittal ring is either cylindrical (with circular transverse section) or angular (commonly with triangular transverse section). In nearly all Stephoidea (with very few exceptions) branches or apophyses are developed from the ring, regularly disposed and often of great morphological importance. Commonly these apophyses are developed in pairs, growing symmetrically on both sides of the ring. The most important of these apophyses are:—(1) Basal apophyses, arising from the basal hole of the ring; (2) mitral apophyses, arising from the apical pole; (3) dorsal apophyses, arising from the middle of the dorsal rod; and (4) ventral apophyses, arising from the middle of the ventral rod. The two former arise in the principal axis, the two latter in the sagittal axis of the body. Very frequently the latter pair is replaced by two pairs of transverse branches, one inferior (mandibular) and one superior (orbital). The apophyses of the ring are either simple or branched, often very large, richly ramified, and give origin to a number of further products.

Whilst in the Stephanida the primary sagittal ring alone represents the whole skeleton, it produces in all other Stephoidea one or more secondary rings. The most important of these is the horizontal basal ring, appearing first in the Semantida (Pl. 92). From the base of the sagittal ring there arise in the horizontal basal plane two pairs of lateral branches or "basal apophyses." The curved opposite branches of the corresponding pairs become united on each side of the primary ring (right and left), and so produce a second, horizontal ring, perpendicular to the former. This basal ring encloses two paired basal gates, which are enclosed on the medial side by the basal rod of the sagittal ring, and on the lateral side by two united apophyses (Semantis, Pl. 92, figs. 1, 2). These two primary basal gates are of the greatest morphological importance; we call them the "jugular gates or jugular pores" (in the description of Bütschli, the pores I, loc. cit., p. 498). The dorsal pair of basal apophyses (on their posterior edge) are the coracal rods, e (rods e of Bütschli); the opposite ventral pair (on their anterior edge) are the clavicular or furcular rods, f (rods e1 of Bütschli); compare Pls. 92-95, and their explanation.

The skeleton of Semantis, the prototype of the Semantida, thus assumes the characteristic form of a signet-ring. The basal ring enclosing the two jugular pores corresponds to the seal-plate. It is commonly more or less horizontal; but often the apophyses descend obliquely (Pl. 92, figs. 1, 2, 13, &c.), more rarely laterally (Pl. 29, fig. 11). The further development of this typical form is essentially effected by the production of new basal pores in the horizontal seal-plate. In Semantrum (Pl. 92, figs. 3, 4, 5) we find already four basal gates. Behind the jugular gates is formed a second pair, the "cardinal gates" (pores II of Bütschli). These are enclosed on the anterior margin by the coracal rods (e), on the posterior margin by the scapular rods (d), a third pair of basal apophyses, arising behind the former from the sagittal ring and uniting with them (the rods e2 of Bütschli). Commonly the two posterior, or cardinal gates are much larger than the two anterior, jugular gates. This characteristic basal plate of Semantrum, with two pairs of basal pores, is of the greatest morphological importance, as it is inherited in by far the greater number of the Nassellaria, though not so generally as Bütschli supposes. The basal ring of Semantrum is either more circular or elliptical, or more polygonal, and is connected with the basal rod of the sagittal ring by three pairs of radial apophyses, the anterior furcular, the middle coracal, and the posterior scapular rods.

A third important form of Semantida is Semantidium (Pl. 92, figs. 6, 7). Here we find three pairs of basal pores in the seal-plate; the third pair, newly formed, consists of the cervical gates (e), bounded in front by the scapular rods (d), behind by a fourth pair of basal apophyses, the cervical rods.

The basal apophyses of the sagittal ring are not only of great morphological importance, because they produce by their union three typical pairs of basal gates or "collar pores," but also because their prolongations often appear as typical basal feet. The distal prolongations of the coracal rods appear in Semantiscus (Pl. 92, figs. 16-18) as two pectoral feet, those of the scapular rods as two tergal feet, whilst the opposite prolongations of the basal rod of the sagittal ring appear as two "sagittal feet" (in front an anterior or sternal, and behind a posterior or caudal foot). In the typical Cortiniscus (Pl. 92, figs. 11-13) only three feet are developed; an odd caudal and two paired pectoral feet (compare above, p. 891). The typical basal ring of the Semantida, with its paired basal gates (Semantis), reappears in the majority of the Coronida, differing from the former in the development of a second vertical ring, which lies in the frontal plane (perpendicular to the sagittal ring), and which we therefore call the frontal ring. In only one small group of the Coronida the basal ring is absent, namely, in the Zygostephanida, and here the frontal ring appears in the simplest form, as a complete elliptical meridian ring, crossing the sagittal ring perpendicularly on the two poles of the main axis (Zygostephanus, Pl. 93, figs. 1-4), Four large lateral gates between the two rings remain open. This form may be derived directly from the Stephanida in the following way; from both poles of a simple sagittal ring there arise two opposite lateral apophyses, which in the frontal plane become curved one towards the other, and united in the poles of the transverse axis. The basal apophyses would be the coracal rods. But it is also possible that Zygostephanus was derived from Semantis by the loss of the furcular rods.

The three typical rings (or the "dimensive rings") of the Stephoidea appear in their most complete form in the subfamily Trissocyclida (Pl. 93, figs. 7, 13). Here all three rings are undivided and completely developed in the three dimensive planes, perpendicular one to another. Between them there remain eight large open gates; the four superior are the four "lateral gates" of Zygostephanus, the four inferior are the four basal gates of Semantrum. The four latter are originally much smaller than the four former; but in Trissocircus and Trissocyclus (Pl. 93, figs. 10-12) they reach the same size. Therefore all eight gates are here of equal form and similar size, and the basal ring, now a true equatorial ring, divides the two meridional rings into two equal halves.

In the Eucoronida, a third subfamily of Coronida, the sagittal and the basal rings are complete, but the frontal ring is incomplete, its basal part being wanting (Pl. 82, figs. 4-6). Therefore we find here six large gates between the three rings; four upper lateral gates (between the two crossed vertical rings) and two lower basal gates (between the basal rod of the sagittal ring and the two halves of the basal ring). Eucoronis, the type of this subfamily, may be derived either directly from Semantis by development of a frontal ring, or from Tristephanium by loss of the basal part of the frontal ring.

A quite simple basal ring with a single gate, distinguishes the fourth subfamily of Coronida, the Acanthodesmida (sensu restricto), the genera Coronidium (Pl. 82, figs. 1, 2, 7, 8) and Acanthodesmia (Pl. 93, fig. 5). The horizontal basal ring alone is here complete, whilst both vertical rings (the sagittal and frontal rings) are incomplete, their basal parts being wanting. Therefore there are here five gates, four lateral and one basal. These forms may be derived from Eucoronis by loss of the basal rod of the primary sagittal ring.

The Tympanida, the fourth family of Stephoidea, exhibit another type of ring structure. Here two parallel horizontal rings are constantly developed, one on the apical pole, the other on the basal pole of the sagittal ring. The latter is the same basal ring as in the Semantida and Coronida. The former is a "mitral ring," developed in the same manner, by union of two pairs of horizontal lateral branches, which arise on both sides from the apical rod (or mitral rod) of the sagittal ring. In the simplest case these two parallel horizontal rings are connected only by the sagittal ring, which is either complete (Protympanium, Pl. 93, fig. 14) or incomplete (Parastephanus, Pl. 93, fig. 21). But commonly also an incomplete frontal ring is present, so that the two horizontal rings are connected by four vertical or subvertical rods; two of these "columellæ" are the dorsal and ventral rods of the sagittal ring, the two others are the lateral rods of the frontal ring. Between the former and the latter are sometimes developed two, four, or more accessory columellæ (probably halves of accessory incomplete diagonal meridian rings). In this way arise the characteristic "drum-forms" of many Tympanida, in which the two parallel horizontal rings correspond to the upper and lower rings of a drum, whilst the connecting vertical columellæ correspond to its parallel lateral rods (Pl. 83, figs. 1, 2, &c.).

Originally the two horizontal rings of these "drum-shells" are both bisected by the complete sagittal ring, each provided with two lateral gates (Protympanida). But in the Eutympanida both rings exhibit one simple gate only, the apical and the basal rod of the sagittal ring being lost. In the Paratympanida both rings are closed by a secondary lattice-plate whilst in the Dystympanida the upper (mitral) ring alone is closed by such a plate, the lower (basal) ring is open. In some Eutympanida the shell assumes the strange form of a regular geometrical cube, the twelve edges of which are represented by thin rods of silex (Lithocubus)—its four upper edges represent the mitral ring, the four lower the basal ring; two opposite of the four vertical cube-edges are the lateral halves of the frontal ring, the two other alternate ones are the remaining halves of the reduced sagittal ring (dorsal and ventral rod) (Pl. 82, fig. 12).

In many Tympanida and Coronida a loose irregular lattice or framework is developed, which partly closes the large open gates. But this never reaches the completeness of a true lattice-shell, such as we find in the Spyroidea, Botryodea, and Cyrtoidea. In by far the greater number of Stephoidea the corners, and partly also the rods, of the shell are armed with numerous irregular spines, often forked or richly branched. Among these spines the descending "basal apophyses" possess a peculiar importance, since by their regular number and disposition they correspond to the radial rods of the Plectoidea, and to the typical "feet" of the Spyroidea and Cyrtoidea. The most important of them are the three cortinar feet (one caudal and two pectoral) of Cortina, Cortiniscus, &c. (compare above, p. 891).

The Central Capsule exhibits in the Stephoidea the same characteristic structure as in all other Monopylea, first exactly pointed out by Richard Hertwig in 1879 (Organismus der Radiol., p. 71, Taf. vii. figs. 4, 5). Its form is commonly ovate or ellipsoidal, sometimes also lentelliptical or nearly spherical. It exhibits constantly on the basal pole the porochora or porous area, and in the basal half the podoconus or pseudopodial cone. From the surrounding sagittal ring it is separated by a thick jelly-like calymma, which commonly exhibits numerous zooxanthellæ. The numerous pseudopodia are commonly branched, with rather rare anastomoses. The membrane of the central capsule is thick.

Synopsis of the Families of Stephoidea.

I. Skeleton composed of the simple vertical sagittal ring only, without secondary rings,	1. Stephanida.
II. Skeleton composed of two crossed rings, a vertical sagittal and a horizontal basal ring,	2. Semantida.
III. Skeleton composed of two crossed vertical meridional rings (a primary sagittal and a secondary frontal ring), commonly also with a horizontal basal ring,	3. Coronida.
IV. Skeleton composed of two parallel horizontal rings (upper mitral and lower basal ring), both connected by a vertical sagittal ring (and often by a vertical frontal ring),	4. Tympanida.

Family XLVIII. Stephanida, Haeckel (Pl. 81).

Monostephida, Haeckel, 1881, Prodromus, p. 447.

Definition.—Stephoidea with a simple sagittal ring, without any lattice-work.

The family Stephanida is the most simple of all Stephoidea, and probably the common ancestral group of this suborder (compare above, p. 933). The skeleton consists of a simple ring only, surrounding the central capsule, and armed commonly with simple thorns or with larger branched spines. The branches of these spines are constantly free, never joining together. Therefore the shell exhibits no trace of fenestration or lattice-work, no pores or gates, except the simple large gate of the ring itself. In all other Stephoidea we find secondary gates or lattice-work.

The first known form of this family is Lithocircus annularis, described by Johannes Müller in 1858 (Abhandl. d. k. Akad. d. Wiss. Berlin, p. 29, Taf. i. fig. 1). He observed already the central capsule ("Blase") surrounded by the circular ring of silex, and the calymma ("Strahlige Gallert") enveloping the whole body. The peculiar structure of the soft body, particularly the "area porosa" on the basal pole of the central capsule, and the pseudopodial cone within it, were first accurately described by Hertwig (in 1879). A great number of simple rings, similar to these, were found in the Challenger collection, and are here arranged in six genera and forty-eight species.

The simple ring of silex, which alone forms the skeleton of the Stephanida, corresponds to the primary or sagittal ring of the other Stephoidea, and lies therefore vertically in the median or sagittal plane of the body. We can therefore distinguish on it four different segments, rods or bows, two of which are more horizontal, two more vertical. The former are one upper bow or apical rod, and one lower bow or basal rod. The latter are one posterior bow or dorsal rod, and one anterior bow or ventral rod. Sometimes each of these four component bows is distinguished by a corner-spine, or by a pair of divergent branches.

In the two simplest (and probably oldest) genera of Stephanida, in Archicircus and Lithocircus, the dorsal and ventral rods of the ring are equal and cannot be distinguished; therefore the fundamental form is here amphithect, diphragmatic, or biradial (the poles of the sagittal axis being equal). In the four other genera the dorsal rod is more straight (often vertical) and more or less different from the ventral, convexly curved rod; therefore the fundamental form is here dipleuric or bilateral, as in the greater number of all Nassellaria (the poles of the sagittal axis being unequal). The general form of the ring in this latter case is commonly obliquely ovate or nearly triangular, the basal pole being more pointed, the apical pole more rounded (Pl. 81).

The rods or bows of the ring are either roundish or cylindrical (with circular or elliptical transverse section), or they are prismatic or angular (commonly with triangular transverse section). In the latter case one edge usually is prominent in the sagittal plane (on the convex outside of the ring), whilst two other edges diverge laterally on both sides of it. The inner or concave margin of the ring is commonly smooth.

The inner perimeter of the large gate, enclosed by the ring, is commonly rounded (elliptical or ovate), rarely angular. However, the outer perimeter of the ring is nearly always polygonal, with prominent corners, and usually from these arise thorns or branched spines which are regularly disposed. Regarding this disposition we may distinguish three cases: A, the spines lie in the sagittal plane and form a single row, arising from the median edge; B, the spines lie on both sides of the latter and form two parallel rows, arising from the two lateral edges; C, the spines represent a combination of A and B, and are disposed in three rows, two paired rows arising from the two lateral edges, and an odd middle row between them, arising from the median edge. The spines are simple, without branches, in Archicircus and Zygocircus; more or less branched in Lithocircus and Dendrocircus. The branches are often richly ramified or arborescent, and exhibit great variety in size, special form, and direction (compare Pl. 81).

The number and disposition of the spines or groups of spines are usually constant, and may be employed in the further progress of our knowledge, to distinguish a number of genera and subgenera. Very commonly (perhaps in the majority of the Stephanida) we find six groups of spines, an apical group on the upper rod of the sagittal ring, a basal group on the lower rod (on the porochora of the central capsule), two ventral groups on the anterior rod, and two dorsal groups on the posterior rod. In other species we find four or eight groups instead of six, and sometimes a larger number.

The most important of these apophyses of the ring are the basal spines, arising from its basal pole, where the porochora of the central capsule rests upon it. They are often much larger and more branched than the other spines, and attain a peculiar morphological value in the small subfamily Cortinida. Here we find three or four regularly disposed "basal spines," which may be compared to the typical "basal feet" of the Cyrtellaria, appearing in the majority of Spyroidea and Cyrtoidea. Cortina, one of the most important Nassellaria, bears three typical divergent feet on the base of the simple ring, two paired anterior or "pectoral feet," and an odd posterior or "caudal foot." The latter appears as a direct basal prolongation of the dorsal rod of the ring, and is opposed to an upper prolongation of the same, which corresponds to the "apical horn" of the Cyrtellaria (Pl. 97, figs. 1-3). As already explained above, these three basal feet of Cortina possess the highest phylogenetic value, since they may also be compared with the three primary radial spines of the Plectoidea, and so connect the Cyrtellaria and the Plectellaria. Stephanium differs from Cortina in the possession of four basal feet, an odd anterior or "sternal foot" being added to the three typical feet of the latter (Pl. 92, figs. 20, 21). Some forms of Plectoidea (Plagoniscus, Plectaniscus, &c.) seem to be nearly related to these Cortinida, and may be easily transformed into them by development of a complete ring, embracing the central capsule. They seem to demonstrate the near affinity of all these triradiate Nassellaria (Pl. 91, figs. 4, 5, 9, 10).

Synopsis of the Genera of Stephanida.

I. Subfamily Lithocircida. No typical basal feet on the base of the ring (no cortinar feet).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Ring diphragmatic or amphithect; dorsal and ventral bow equal.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Ring smooth or thorny, without branched spines.	401. Archicircus.
				Ring armed with branched spines,	402. Lithocircus.
		Ring dipleuric, bilateral; dorsal and ventral bow different.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Ring smooth or thorny, without branched spines,	403. Zygocircus.
				Ring armed with branched spines.	404. Dendrocircus.
II. Subfamily Cortinida. Three or four typical basal feet on the ring (cortinar feet).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Three basal feet (and an apical horn).		One caudal and two lateral feet,	405. Cortina.
		Four basal feet (and an apical horn).		Two sagittal and two lateral feet,	406. Stephanium.

Subfamily 1. Lithocircida, Haeckel.

Definition.—Stephanida without typical basal feet or cortinar feet.

Genus 401. Archicircus,^[1] n. gen.

Definition.—Stephanida with a simple amphithect or diphragmatic ring, smooth or thorny, without branched spines and basal feet.

The genus Archicircus is the most primitive and simplest form of all Stephoidea, and probably the common ancestral form, not only of this suborder, but of the greater number of all Nassellaria (compare above, p. 893). The skeleton consists only of a quite simple sagittal ring, in which commonly a slight difference of both poles of the main axis (basal and apical pole) is visible, but no difference between the dorsal and the ventral bow of the ring. In my Prodromus (1881, p. 447) the species of Archicircus were disposed partly in the subgenus Monostephus, partly in the genus Lithocircus.

Subgenus 1. Monostephus, Haeckel, 1881, Prodromus, p. 447.

Definition.—Ring circular, elliptical, or ovate, without prominent corners.

1. Archicircus princeps, n. sp.

Gate circular. Ring circular, smooth, its transverse section also circular. The simplest form of all Stephoidea.

Dimensions.—Diameter of the gate 0.05 to 0.08; thickness of the ring 0.006 to 0.008.

Habitat.—Central Pacific, Stations 265 to 274, depth 2350 to 2925 fathoms.

2. Archicircus monostephus, n. sp. (Pl. 83, fig. 17).

Gate circular. Ring circular, with three elegantly denticulate edges (one outer median and two lateral edges). Transverse section of the ring triangular.

Dimensions.—Diameter of the gate 0.06 to 0.08; thickness of the ring 0.01 to 0.008.

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

3. Archicircus ellipsis, n. sp.

Gate elliptical. Ring elliptical, on the inner margin smooth, on the outer margin with fifteen to twenty equal, short, simple, or slightly forked thorns. Transverse section ovate.

Dimensions.—Diameter of the gate 0.05 to 0.09; thickness of the ring 0.01 to 0.014.

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

4. Archicircus ovalis, n. sp.

Gate ovate. Ring elliptical, smooth, with three prominent, slightly distorted edges, without thorns; in the transverse section triangular.

Dimensions.—Diameter of the gate 0.08 to 0.12; thickness of the ring 0.006 to 0.009.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

5. Archicircus monopylus, n. sp.

Gate ovate. Ring ovate, thorny, with three distorted edges, in the transverse section triangular; surface covered with numerous simple small thorns arising from the three edges.

Dimensions.—Diameter of the gate 0.1 to 0.15; thickness of the ring 0.01 to 0.012.

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

Subgenus 2. Archistephus, Haeckel.

Definition.—Ring polygonal, with four to six or more prominent corners (and commonly with simple spines arising from the corners).

6. Archicircus quadratus, n. sp.

Gate square. Ring square, with three edges and four short simple pyramidal spines on the four corners, opposite in pairs in two perpendicular diameters. Transverse section triangular.

Dimensions.—Diameter of the gate 0.08; thickness of the ring 0.008.

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

7. Archicircus rhombus, n. sp. (Pl. 81, fig. 7).

Gate rhombic. Ring rhombic, with four prominent edges and four pairs of short, divergent, pyramidal spines on the four corners, arising from the lateral edges of the four rods, about as long as the radius of the gate.

Dimensions.—Diameter of the gate 0.04 to 0.08; thickness of the ring 0.007 to 0.01.

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

8. Archicircus duodenus, n. sp.

Gate square or rhombic. Ring rhombic, with three prominent edges and twelve stout and straight pyramidal spines, about as long as the radius of the gate. In each of the four corners are three divergent spines, arising from the three edges of each two meeting rods.

Dimensions.—Diameter of the gate 0.08; thickness of the ring 0.012.

Habitat.—North Atlantic, surface (Rabbe).

9. Archicircus primordialis, n. sp. (Pl. 81, fig. 1).

Gate ovate. Ring hexagonal, with three prominent edges and six short pyramidal thorns at the six corners; the basal thorn is either simple or forked.

Dimensions.—Diameter of the gate 0.07; thickness of the ring 0.01 to 0.015.

Habitat.—Central Pacific, Stations 265 to 274, depth 2350 to 2925 fathoms.

10. Archicircus hexacanthus, n. sp. (Pl. 81, fig. 4).

Gate subregular, hexagonal. Ring hexagonal, with three sharp edges and six equal radial pyramidal spines, arising from the six corners and placed in the plane of the ring, about as long as the diameter of the gate.

Dimensions.—Diameter of the gate 0.05 to 0.07; thickness of the ring 0.01.

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

11. Archicircus hertwigii, Haeckel.

Lithocircus annularis, R. Hertwig (non J. Müller), 1879, Organismus der Radiol., p. 69. Taf. vii. fig. 5.

Gate hexagonal, with prolonged main axis. Ring hexagonal, with two prominent edges and six pairs of equal, short, conical spines, arising from the two edges of the six rods at the six corners and divergent on each side of the plane of the ring. The basal spine-pair is doubled, therefore there are in all fourteen spines.

Dimensions.—Diameter of the gate 0.05 to 0.07; thickness of the ring 0.005 to 0.006.

Habitat.—Mediterranean (Messina), Hertwig, surface.

12. Archicircus triglyphus, n. sp.

Gate ovate. Ring hexagonal, with three prominent edges and twenty-two to twenty-four simple curved spines, arising from the six corners and about as long as the diameter of the gate. In the basal corner arise six to nine larger spines, protecting the basal pole of the central capsule. From each of the five other corners arise three spines, diverging from the three edges.

Dimensions.—Diameter of the gate 0.07 to 0.11; thickness of the ring 0.008 to 0.011.

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

13. Archicircus sexangularis, n. sp. (Pl. 81, fig. 12).

Gate hexagonal or subcircular. Ring hexagonal, with two sharp prominent edges and six pairs of divergent spines, about as long as the radius of the gate, and arising from the two edges at the six corners. The two apical and the two basal spines are simple and conical, whilst the eight other spines, arising in pairs from the two dorsal and the two ventral corners, are slightly forked.

Dimensions.—Diameter of the gate 0.06 to 0.08; thickness of the ring 0.01 to 0.015.

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

Genus 402. Lithocircus,^[2] J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 484.

Definition.—Stephanida with a simple amphithect or diphragmatic ring, armed with branched spines, without typical basal feet.

The genus Lithocircus is the oldest known form of all Stephoidea, founded by J. Müller in 1856 for his Lithocircus annularis, the first species of this suborder described. We retain here this cosmopolitan form as the typical representative of the genus, which differs from the preceding Archicircus, its ancestral form, in the development of branched radial spines.

1. Lithocircus annularis, J. Müller.

Lithocircus annularis, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 29, Taf. i. fig. 1.

Gate circular. Ring circular, with four forked or simply branched spines, opposite in pairs in two diameters, perpendicular one to the other. Spines with slender curved fork-branches, about as long as the diameter of the gate. The specimen figured by J. Müller bears a supernumerary fifth spine; numerous other specimens observed by me exhibited a regular cross of four spines.

Dimensions.—Diameter of the gate 0.1 to 0.15; length of the spines 0.01 to 0.18.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

2. Lithocircus quadricornis, n. sp. (Pl. 81, fig. 9).

Gate square. Ring square, with three sharp denticulate edges, and four large bunches of richly branched spines on the four corners. In each corner arise three curved spines, about as long as the diameter of the ring; their numerous irregular branches are forked and curved like the antlers of deer.

Dimensions.—Diameter of the gate 0.07; length of the horns 0.06 to 0.09.

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

3. Lithocircus decimalis, n. sp. (Pl. 81, fig. 15).

Gate elliptical. Ring pentagonal, with three prominent edges and five pairs of branched spines on the five corners. In each corner arise two or three curved spines, about as long as the radius of the gate, each with two to four forked branches.

Dimensions.—Diameter of the gate 0.08; length of the spines 0.03 to 0.05.

Habitat.—North Atlantic, Station 354, surface.

4. Lithocircus hexablastus, n. sp. (Pl. 81, fig. 17).

Gate elliptical. Ring hexagonal, with three prominent edges and six pairs of branched spines, arising from the six corners. Each of the twelve spines is short and stout, only half as long as the radius of the gate, and bears a bunch of ten to twenty short, densely aggregated, conical or horn-like curved branches.

Dimensions.—Diameter of the gate 0.1; length of the spines 0.02 to 0.03.

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

5. Lithocircus crambessa, n. sp. (Pl. 81, fig. 6).

Gate elliptical or subcircular. Ring hexagonal, with three wing-shaped distorted edges and six groups of branched spines, arising from the six corners. In each corner arise three short and stout divergent spines, each bearing a bunch of numerous short roundish branches like a cauliflower, scarcely as long as the thickness of the ring.

Dimensions.—Diameter of the ring 0.1 to 0.12, length of the spines 0.01 to 0.02.

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

6. Lithocircus tarandus, n. sp. (Pl. 92, fig. 19).

Gate circular. Ring hexagonal, with three sharp edges and six pairs of large branched spines, arising from the flat lateral edges on the six corners. Each of the twelve spines is horizontally expanded, longer than the diameter of the ring and dichotomously forked like the antlers of a reindeer. If the lateral ends of the branches of this species become united in the frontal plane, we get Microcubus, the four upper spines forming the mitral ring, the four middle the equatorial ring, and the four lower the basal ring.

Dimensions.—Diameter of the gate 0.08; length of the spines 0.09.

Habitat.—Central Pacific, Station 272, surface.

7. Lithocircus furcatus, n. sp.

Gate ovate. Ring ovate, with three sharp prominent edges. The two lateral edges are smooth. The median edge (in the sagittal plane) bears sixteen to twenty forked spines (commonly eight dorsal, eight ventral, and four basal). All the spines are of nearly equal size, slightly curved, and about half as long as the short sagittal axis of the ring.

Dimensions.—Diameter of the gate 0.08 to 0.12; length of the spines 0.03 to 0.04.

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

8. Lithocircus magnificus, n. sp. (Pl. 81, fig. 16).

Gate ovate or nearly elliptical. Ring ovate, with three prominent edges, and numerous richly branched spines arising from the three edges. The specimen figured, which I observed living in the Mediterranean, exhibited eight bunches of larger spines, three dorsal, three ventral, one apical, and one basal bunch; the latter much larger than the seven others. Each bunch was composed of two to four larger and numerous smaller spines, their branches curved and forked. The ovate purple central capsule, with a distinct podoconus, filled more than the half of the gate.

Dimensions.—Diameter of the gate 0.1 to 0.13; length of the spines 0.05 to 0.15.

Habitat.—Mediterranean (Portofino, 1880), Atlantic (Canary Islands), Station 354, surface.

Genus 403. Zygocircus,^[3] Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 496.

Definition.—Stephanida with a simple dipleuric or bilateral ring, smooth or thorny, without branched spines and basal feet.

The genus Zygocircus and the following Dendrocircus differ from the two preceding older genera in the bilaterally symmetrical or dipleuric form of the sagittal ring. Whilst in Archicircus and Lithocircus the two sagittal halves or bows of the ring, the dorsal and ventral bow, are equal (therefore the fundamental form amphithect or diphragmatic), here both bows become distinctly different; the dorsal bow is constantly more straight (often vertical), the ventral bow more convex (obliquely ascending). This dipleuric differentiation is most important, as it is transmitted to the greater number of Nassellaria by heredity.

1. Zygocircus sagittalis, n. sp.

Gate ovate. Ring half ovate or nearly triangular, with three curved edges and three prominent corners, one apical and two basal protuberances. Dorsal rod vertical, twice as long as the horizontal basal rod. Ventral rod convexly curved.

Dimensions.—Diameter of the gate 0.05 to 0.07; height of the tubercles 0.01 to 0.015.

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

2. Zygocircus trigonus, n. sp.

Gate triangular. Ring triangular, with three curved edges and three prominent corners, which are prolonged into nine divergent conical spines; three spines arising from the three edges of each corner. Dorsal rod vertical; ventral and basal rods curved and convergent.

Dimensions.—Diameter of the gate 0.11 to 0.13; length of the spines 0.01 to 0.015.

Habitat.—Indian Ocean, Sunda Archipelago (Rabbe), surface.

3. Zygocircus tetragonus, n. sp.

Gate ovate. Ring quadrangular, without edges, with four simple conical spines of different sizes; one smaller apical, one larger basal, and two equatorial spines of middle size (one dorsal and one ventral). Dorsal and ventral rod curved.

Dimensions.—Diameter of the gate 0.04 to 0.06; length of the spines 0.018 to 0.026.

Habitat.—Tropical Atlantic, Station 338, depth 1990 fathoms.

4. Zygocircus rhombicus, n. sp.

Gate rhombic. Ring rhombic, with three prominent edges, and eight short conical curved spines arising from the lateral edges at the four corners of the rhombus. The basal and ventral spine are larger than the apical and dorsal spine; the ventral rod is more curved (with smaller angle) than the shorter dorsal rod. The medial edge of the ring is smooth, without spines.

Dimensions.—Diameter of the gate 0.08; length of spines 0.02 to 0.04.

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

5. Zygocircus pentagonus, n. sp. (Pl. 81, fig. 8).

Gate roundish pentagonal. Ring very thick (about as thick as the radius of the gate), irregularly pentagonal, with prominent sagittal edge. On both sides of the latter arise at the five corners five pairs of short simple irregularly curved spines. The four ventral spines are larger than the four dorsal, and the two basal spines larger than the eight former, forked. (In fig. 8 the basal spines are turned upwards.)

Dimensions.—Diameter of the gate 0.07; length of the spines 0.04 to 0.06.

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

6. Zygocircus hexagonus, n. sp.

Gate irregularly hexagonal. Ring obliquely hexagonal, thick, without edges, with six short and stout conical spines on the six corners. The two spines of the curved ventral rod are longer than the two spines of the straight dorsal rod. The apical spine is smaller and the basal spine larger than the four others.

Dimensions.—Diameter of the gate 0.07 to 0.09; length of the spines 0.01 to 0.03.

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

7. Zygocircus triquetrus, n. sp. (Pl. 81, fig. 3).

Gate obliquely ovate. Ring obliquely hexagonal, with three sharp edges and three short conical spines on each of the six corners. Therefore each hexagonal edge bears six short radial spines of equal size.

Dimensions.—Diameter of the gate 0.04 to 0.08; length of the spines 0.01 to 0.02.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

8. Zygocircus dodecanthus, n. sp.

Gate semicircular. Ring semicircular or irregularly hexagonal, without edges, with twelve short blunt spines, arising in pairs from the six corners; two apical, two basal, and between them two equatorial corners. Three pairs of spines remain on the straight dorsal rod, three on the curved ventral rod.

Dimensions.—Diameter of the gate 0.04 to 0.06; length of the spines 0.01 to 0.02.

Habitat.—Central Pacific, Stations 263 to 268; depth 2650 to 2900 fathoms.

9. Zygocircus acacia, n. sp. (Pl. 81, fig. 5).

Gate obliquely ovate. Ring semi-ovate, with straight dorsal and curved ventral rod, partly with distorted edges. Six bunches of numerous short and straight conical spines arise from the ring, one larger bunch (often trifid) from the apex, two smaller bunches from the dorsal, two from the ventral rod, and one very large bunch from the base. The six bunches are often more separated, smaller, and the spines shorter than in the figured specimen, which passes over into Dendrocircus.

Dimensions.—Diameter of the gate 0.12 to 0.16; length of the spines, 0.01 to 0.07.

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

10. Zygocircus polygonus, n. sp. (Pl. 81, fig. 2).

Gate irregularly roundish or ovate. Ring irregularly polygonal or sometimes nearly circular, without edges, armed with a single series of ten to fifteen short pyramidal spines, which are irregularly disposed in the sagittal plane. The ventral rod is strongly curved, often semicircular, the dorsal rod less curved or nearly straight.

Dimensions.—Diameter of the gate 0.05 to 0.07; length of the spines 0.004 to 0.02.

Habitat.—Cosmopolitan—Atlantic, Pacific; also fossil in Barbados.

11. Zygocircus bütschlii, n. sp.

Zygocircus productus, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 497.

Gate obliquely ovate. Ring irregularly roundish, semi-ovate or ovate, with interrupted and distorted edges, and with a large number (ten to twenty or more) of simple, irregularly formed and asymmetrically disposed spines; commonly some larger spines at the base.

Dimensions.—Diameter of the gate 0.05 to 0.09; length of the spines 0.005 to 0.02.

Habitat.—Fossil in Barbados.

12. Zygocircus productus, Bütschli.

Zygocircus productus, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi p. 496. Lithocircus productus, R. Hertwig, 1879, Organismus d. Radiol., p. 69, Taf. vii. fig. 4.

Gate obliquely ovate. Ring obliquely ovate, with three complete prominent edges and with numerous (ten to twenty or more) simple, short conical spines, arising in three series from the three edges; commonly some smaller spines at the base.

Dimensions.—Diameter of the gate 0.1 to 0.2; length of the spines 0.005 to 0.02.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

Genus 404. Dendrocircus,^[4] Haeckel, 1881, Prodromus, p. 447.

Definition.—Stephanida with a simple dipleuric or bilateral ring, armed with branched spines, without typical basal feet.

The genus Dendrocircus has the same dipleuric or bilaterally symmetrical form of the sagittal ring as its ancestral genus Zygocircus. It differs from the latter in the development of branched radial spines, and therefore bears to it the same relation as the amphithect Lithocircus does to the simpler Archicircus.

1. Dendrocircus quadrangulus, n. sp.

Gate irregularly quadrangular or nearly semicircular. Ring quadrangular, edgeless, with four unequal sides; ventral rod more curved and with longer sides than the dorsal rod. From the four edges arise four strong, irregularly branched spines, about as long as the diameter of the gate, with curved branches; the ventral and basal spines larger than the dorsal and apical spines. Similar to Lithocircus quadricornis (Pl. 81, fig. 9), but less branched, and with a striking difference between the shorter dorsal and the longer ventral rod.

Dimensions.—Diameter of the gate 0.04 to 0.06; length of the spines 0.05 to 0.07.

Habitat.—North Pacific, Station 256, depth 2950 fathoms.

2. Dendrocircus dodecarrhiza, n. sp.

Gate obliquely ovate. Ring irregularly quadrangular, with three prominent edges. From the latter arise at the four corners twelve divergent, irregularly branched spines (three in each corner), about as long as the radius of the gate, with curved branches; the three basal spines larger than the nine others.

Dimensions.—Diameter of the gate 0.08 to 0.1; length of the spines 0.04 to 0.06.

Habitat.—Indian Ocean (Maldive Islands), surface (Haeckel).

3. Dendrocircus dodecancistra, n. sp. (Pl. 81, fig. 11).

Gate obliquely ovate or nearly elliptical. Ring irregularly ovate, with three distorted edges and six pairs of branched spines. The two ventral pairs are much more distant than the two dorsal pairs, the ventral rod being longer and more curved than the dorsal rod. All twelve spines are of nearly equal size, are more or less curved, about as long as the diameter of the gate, and each bears six to twelve irregular short branches at the end.

Dimensions.—Diameter of the gate 0.07 to 0.08; length of the spines 0.05 to 0.08.

Habitat.—Tropical Atlantic, Station 342, depth 1445 fathoms.

4. Dendrocircus arborescens, n. sp. (Pl. 81, fig. 10).

Gate irregularly roundish or nearly circular. Ring of the same form, with slight edges and six pairs of elegant arborescent spines (one apical, two dorsal, two ventral, and one basal pair); the three latter somewhat larger than the three former. Each tree is larger than the ring, in the basal half simple, in the distal half forked, each fork-branch with numerous dichotomous terminal branches.

Dimensions.—Diameter of the gate 0.06 to 0.08; length of the spines 0.12 to 0.15.

Habitat.—Central Pacific, Stations 266 to 274, surface.

5. Dendrocircus elegans, n. sp. (Pl. 81, fig. 13).

Gate irregularly ovate. Ring thick, ovate, with three denticulate edges and six bunches of stout, branched and spinulate, curved spines. The four ventral spines are more distant than the four dorsal, the ventral rod being more curved than the dorsal. The latter bears above the two apical spines. The two basal spines are much larger, deeply forked; their four fork-branches may be compared to the four basal feet of Stephanium.

Dimensions.—Diameter of the ring 0.09 to 0.11; length of the spines 0.03 to 0.06.

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

6. Dendrocircus barbadensis, n. sp.

Gate irregularly ovate or nearly semicircular. Ring of the same oblique form, thick, with interrupted and distorted edges, armed with eight to twelve larger irregularly formed and branched acute spines; between them numerous conical smaller spines. This common species is very polymorphous and variable.

Dimensions.—Diameter of the ring 0.05 to 0.08; length of the spines 0.005 to 0.02.

Habitat.—Fossil in Barbados.

7. Dendrocircus stalactites, n. sp. (Pl. 81, fig. 14).

Gate obliquely ovate. Ring irregularly ovate or roundish, very thick, without edges, armed with numerous (eight to twelve or more) short and stout branches, which are shorter than the diameter of the gate, irregularly disposed and branched, with very numerous clustered blunt ramules.

Dimensions.—Diameter of the gate 0.07 to 0.09; length of the spines 0.02 to 0.06.

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

Subfamily 2. Cortinida, Haeckel.

Definition.—Stephanida with typical basal feet (or cortinar feet).

Genus 405. Cortina,^[5] n. gen.

Definition.—Stephanida with a simple dipleuric or bilateral ring, bearing at the base three divergent feet (one odd caudal and two paired lateral feet).

The genus Cortina and the following Stephanium represent together the small but very important group of Cortinida, differing from the simple Lithocircida in the possession of three typical basal feet, which are transmitted to the majority of the Nassellaria by heredity, and produce their peculiar triradial structure. They appear therefore as a combination of the simple ring (Zygocircus) with three basal feet (Plagonium). One of these three divergent feet is the odd caudal foot, opposite to the apical horn; the two others are the paired lateral or pectoral feet. (On the probable origin and the typical signification of Cortina compare above, pp. 891-894.)

1. Cortina tripus, n. sp. (Pl. 83, fig. 9).

Ring ovate, smooth, or with a few short thorns. Apical horn oblique, curved, simple, smooth, about as long as the sagittal axis of the ring. Feet divergent, curved, simple, smooth, about as long as the horn; the caudal foot shorter than the two pectoral feet. Very variable in form and size.

Dimensions.—Height of the ring 0.06 to 0.09, breadth 0.04 to 0.06; length of the feet 0.05 to 0.1.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, surface and in various depths.

2. Cortina typus, n. sp. (Pl. 97, fig. 1).

Ring kidney-shaped or nearly semicircular, with revolute vertical dorsal rod and strongly curved ventral rod; both rods with two pairs of spine-bunches. Apical horn nearly straight, thorny, longer than the ring, directed a little obliquely backwards. Feet slightly curved, of equal length, two to three times as long as the ring; each armed with few large bunches of curved spines, which are more developed in the caudal foot than in the two pectoral feet.

Dimensions.—Height of the ring 0.14, breadth 0.08; length of the feet 0.2 to 0.3.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

3. Cortina conifera, n. sp.

Ring subcircular, smooth. Apical horn and the three divergent feet of equal size and similar form, cylindrical, straight, about as long as the ring, at the distal end thickened, with a dimply cone (similar to Tripospyris conifera and Tripospyris eucolpa, Pl. 84, figs. 4, 7).

Dimensions.—Height of the ring 0.08, breadth 0.06; length of the feet 0.09.

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

4. Cortina furcata, n. sp.

Ring elliptical, with three forked horizontal spines (one on the dorsal and two on the ventral rod). Apical horn and the three divergent feet of equal size, somewhat longer than the ring, slightly curved, in the distal half forked.

Dimensions.—Height of the ring 0.07, breadth 0.05; length of the feet 0.09.

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

5. Cortina dendroides, n. sp.

Ring ovate, with six pairs of branched horizontal spines, three on the dorsal and three on the ventral rod. Apical horn very large, arborescent, about as long and as broad as the ring. Feet similar to the horn, also richly branched, of equal size. All the rods and their branches curved, with prominent distorted edges.

Dimensions.—Height of the ring 0.13 to 0.17, breadth 0.1 to 0.12; length of the feet 0.15 to 0.2.

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

6. Cortina cervina, n. sp. (Pl. 92, fig. 21).

Ring ovate, with four pairs of forked horizontal spines (two dorsal and two ventral pairs). Apical horn straight and stout, as long as the ring, with trifid point. Three feet equal, widely divergent, very large, branched like a deer's antler, with very numerous short and stout, curved and pointed branches. All rods and branches roundish, without edges.

Dimensions.—Height of the ring 0.1, breadth 0.07; length of the feet 0.12 to 0.16.

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

Genus 406. Stephanium,^[6] n. gen.

Definition.—Stephanida with a simple dipleuric or bilateral ring, bearing at the base four divergent feet (two sagittal and two lateral feet).

The genus Stephanium differs from the preceding nearly allied Cortina in the production of four basal feet; the new foot, missing in the latter, is the anterior or sternal foot. Therefore Stephanium may be regarded as the archetype of all those Nassellaria in which, on the base of the sagittal ring, there are developed four typical feet—two sagittal feet (the posterior caudal and anterior sternal foot) and two lateral feet (right and left). On the origin of Stephanium compare above, p. 893, &c.

1. Stephanium quadrupes, n. sp. (Pl. 92, fig. 20).

Ring ovate, with three prominent dentate edges and a short pyramidal apical horn. Four feet all of nearly equal size, about as long as the ring, also with three thorny edges, in the upper half divergent, in the lower convergent.

Dimensions.—Height of the ring 0.12, breadth 0.08; length of the feet 0.11 to 0.13.

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

2. Stephanium tetrapus, n. sp.

Ring elliptical, without edges, thorny, with a stout, thorny apical horn of the same length. Four feet curved and irregularly branched, divergent, of different size. The two sagittal feet (the anterior sternal and posterior caudal) about as long as the ring. The two lateral feet (right and left) nearly twice as long, more richly branched.

Dimensions.—Height of the ring 0.16, breadth 0.11; length of the feet 0.15 to 0.3.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms. Fossil in Barbados.

Family XLIX. Semantida, n. fam.

Definition.—Stephoidea with a single vertical ring (the primary sagittal ring), bearing on its base a horizontal ring (basal or cortinar ring) with two to four or more basal gates (or cortinar pores).

The family Semantida differs from the preceding Stephanida in the development of a small horizontal ring on the base of the primary vertical sagittal ring. By the crossing of these two rings a small latticed basal plate is formed, with one or two pairs of pores; rarely with a greater number of "basal pores." The production of this characteristic "basal plate" is of the greatest morphological importance, as the beginning of the numerous different lattice-formations, which are differentiated in the great majority of Nassellaria.

In my Prodromus (1881, p. 446) I had enumerated the Semantida with three genera (Nos. 298 to 300) as a separate subfamily of the Dyostephida or "Stephoidea biannularia," and characterised these "Dyostephanida" by the following definition: "Skeleto annulis duobus composito, qui in duobus planis invicem perpendicularibus jacent; altero annulo (sagittali) verticali, altero (basali) horizontali." As the names there given were already employed with another signification, and as the Zygostephanida (there united with the Dyostephanida) are more closely related to the Coronida, I now change the names, and propose to call the family Semantida, expressing by this term the typical similarity of the skeleton to a signet-ring (Semantis, Semantrum, Semantidium).

At about the same time, some Stephoidea of this family were accurately described by Bütschli (1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 495, Taf. xxxii. figs. 6, 7, 8). He called them Stephanolithis, a name which Ehrenberg had employed, not for complete shells of Radiolaria, but for isolated parts of such, and for siliceous fragments of different skeletons, needles of Sponges, &c. The three species described by Bütschli represent three different genera of our Semantida, viz., Semantis spinescens (with two gates in the basal plate), Semantrum mülleri (with four gates), and Semantidium haeckelii (with six gates). He pointed out the great morphological value of the fenestrated basal plate and its paired gates, as beginnings of numerous other Nassellaria. But his opinion, that in all Spyroidea and Cyrtoidea, derived from these, two pairs of basal gates were constant, was erroneous, nor was the formation of the first pair naturally explained; he supposed that the formation of the basal plate begins by development of an odd sagittal apophysis, arising from the base of the primary sagittal ring. But this odd sagittal apophysis ("der unpaare mediane Kieselfortsatz c1", loc. cit., p. 497) is in reality not a primary and essential part of the skeleton, but secondary and of little morphological value, absent in the majority of the Semantida and of the other Nassellaria.

We divide our family Semantida into two different subfamilies, which possibly possess a direct phylogenetic relation to the two subfamilies of Stephanida:—The Semantiscida have no typical feet, and have arisen directly from the Lithocircida; the Cortiniscida, however, possess the three typical basal feet of Cortina, and may therefore be derived directly from the Cortinida. Since these three cortinar feet are probably identical with the three primary radial rods of the Plectoidea, an immediate affinity also to these Nassellaria is indicated.

The Semantiscida, which do not possess these three basal cortinar feet, are the simpler forms of the family. The simplest of all, and perhaps the common ancestral form of the whole family, is Semantis (Pl. 92, figs. 1, 2). It may be derived from Archicircus or Zygocircus by development of two pairs of horizontal apophyses on its base, around the porochora of the central capsule. The two rods of each side (right and left), becoming curved one towards the other, and meeting laterally, form a simple horizontal gate, and the two paired basal gates together, a horizontal ring or basal ring, to which the primary sagittal ring is perpendicular. In the next allied genus, Semantrum (Pl. 92, figs. 3-5), three pairs of horizontal apophyses are developed, and therefore two pairs of basal gates produced, an anterior and a posterior. In the third genus, Semantidium (Pl. 92, figs. 6, 7), three pairs of basal pores or gates are visible, surrounded and separated by four pairs of horizontal apophyses, which arise from the base of the sagittal ring. Finally, in Clathrocircus (Pl. 92, figs. 8-10) the number of apophyses is much increased, and two parallel rows of pores are developed along the two sides of the sagittal ring.

The basal plate or the "seal," developed from the base of the primary sagittal ring or "signet-ring," is therefore a horizontal ring, which becomes bisected by the latter, and exhibits either one pair of primary "basal gates" or two or three pairs of these important basal pores, rarely more. Since these pores possess the greatest morphological value, and are probably everywhere homologous, we give to them and to the separating apophyses certain names, and call the anterior pair of gates, "jugular pores" (i in our figures, the pair I of Bütschli); the middle (usually the largest) pair, "cardinal pores" (k in our figures, the pair II of Bütschli), and the posterior, smaller pair, "cervical pores," l. The typical pairs of rods, by the union of which these basal pores arise, are the following:—(1) the clavicular or furcular rods, f, the first pair (rods e1 of Bütschli), (2) the coracal rods, e, between the jugular and cardinal pores (rods e of Bütschli), (3) the scapular rods, g, between the cardinal and cervical pores (rods e2 of Bütschli), (4) the cervical rods, the fourth pair of apophyses, the most posterior, h. Bütschli supposes that the topographical succession of the three typical pairs of basal pores is also the chronological succession, the jugular being formed first, the cardinal second and the cervical pores third but it seems that this succession is often altered and that the cardinal pores (the largest), appear first, the jugular pores (in front of them) second and the cervical pores third (or perhaps sometimes in the inverse succession).

The Cortiniscida, the second subfamily of Semantida, differ from the preceding Semantiscida in the possession of three typical basal feet, which are probably inherited from the Cortinida, and perhaps indirectly from the Plagonida (Plagoniscus). The simplest and the most important form of this second family is Cortiniscus (Pl. 92, figs. 11-13), differing from its probable ancestral form, Cortina, in the development of a basal ring, produced by horizontal union of the basal apophyses. The three typical feet are the same as in all triradiate Nassellaria, two paired pectoral feet (p₁, p₁₁) diverging on the anterior base of the sagittal ring, whilst the odd caudal foot (c) lies on its posterior base in the sagittal plane and appears as a basal prolongation of the dorsal rod of the sagittal ring; the upper part of the dorsal rod is usually prolonged into an ascending apical horn. In Stephaniscus (Pl. 92, figs. 14, 15) four basal feet are visible, an anterior or sternal foot (z) being added as a prolongation of the basal rod of the ring, opposite to the caudal foot. Finally, Semantiscus (Pl. 92, figs. 16-18) is distinguished by the possession of six divergent basal feet, probably identical with those of all six-radiate Nassellaria; three of these may be regarded as primary and perradial, the odd caudal and the paired pectoral feet; the three other intercalated as secondary or interradial feet, the odd sternal (z) and the paired tergal feet (t₁, t₁₁).

The basal plate of these Cortiniscida exhibits the same important differences as in the preceding Semantiscida, either one, or two, or three pairs of basal gates being developed. But there occur also in some species (mainly in Cortiniscus) only three basal gates, an odd anterior (between the two pectoral feet and a connecting horizontal bar), and two paired posterior (between the two pectoral and the odd caudal foot). It requires further accurate researches to solve the important problem, what the true homologies of these typical basal pores and the separating bars are in the different genera of Semantida. In Semantiscus there are three pairs of basal pores in the horizontal seal, corresponding to those of Semantidium and the radial rods or bars between, these are the basal parts of the six radial feet; therefore the odd caudal foot (t) seems to be the posterior, and the odd sternal foot (z) the anterior prolongation of the basal part of the primary sagittal ring; the two paired anterior or pectoral feet (p₁, p₁₁) the prolongations of the coracal rods (e) and the two paired posterior or tergal feet (t₁, t₁₁), the prolongations of the scapular rods (g). But it is not yet certain whether these six radial feet and the separating gates of the basal plate are all the same and truly homologous in all six-radiate Nassellaria. In every case the comparative study of the Semantida is of the highest value for the accurate knowledge of the Monopylea.

Synopsis of the Genera of Semantida.

I. Subfamily Semantiscida. Basal ring without typical, regularly disposed basal feet (no cortinar feet).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Only two, four, or six basal pores (no dorsal and ventral pores).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Two basal pores,	407. Semantis.
				Four basal pores,	408. Semantrum.
				Six basal pores,	409. Semantidium.
		Besides four basal pores, also apical pores or dorsal and ventral pores along the whole ring,			410. Clathrocircus.
II. Subfamily Cortiniscida. Basal ring with typical, regularly disposed basal feet (cortinar feet).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Three basal feet.		One odd caudal foot and two paired lateral feet,	411. Cortiniscus.
		Four basal feet.		Two sagittal and two lateral or pectoral feet,	412. Stephaniscus.
		Six basal feet.		Two sagittal, two pectoral, and two tergal feet,	413. Semantiscus.

Subfamily 1. Semantiscida, Haeckel.

Definition.—Semantida without typical basal feet or cortinar feet.

Genus 407. Semantis,^[7] n. gen.

Definition.—Semantida with two basal pores (or jugular pores), without typical basal feet.

The genus Semantis, the most primitive and the oldest of the Semantida, is of the greatest morphological interest, as the first form of Stephoidea which produces gates or pores by communicating branches, and therefore the probable ancestral form not only of this family, but of the greater number of all Stephoidea, and perhaps even of all Spyroidea and Cyrtoidea. Semantis arises from Archicircus by the production of two pairs of lateral branches from the basilar rod of the sagittal ring, one anterior pair of clavicular rods, and one posterior pair of coracal rods. By junction of the clavicular and coracal rod on each side arises a left and a right pore, the "jugular pore or jugular gate."

1. Semantis biforis, n. sp. (Pl. 92, fig. 2).

Sagittal ring obliquely ovate, nearly trapezoidal, with six pairs of short mammillated knobs or branches; dorsal rod straight, vertical, with two pairs of knobs, ventral rod strongly convex, also with two pairs of knobs; two other pairs in the apical rod. Basilar rod horizontal, straight. Basal ring with six pairs of similar knobs, three on each side. Basal gates ovate or nearly triangular.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.07.

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

2. Semantis distoma, n. sp.

Sagittal and basal ring nearly of the same form as in the preceding species, but half as thick and armed with numerous branched spines which are about half as long as the diameter of the main gate, and with thin and curved pointed branches.

Dimensions.—Height of the sagittal ring 0.11, breadth 0.08.

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

3. Semantis dipyla, n. sp.

Sagittal ring kidney-shaped, very thick, with six pairs of short, thorny, or irregularly tuberculated knobs (two dorsal, two apical, and two ventral pairs). Basal ring smooth, scarcely half as thick, horizontal, with two semicircular basal gates, about half as broad as the main gate. From the two opposite lateral corners of the basal ring two slender upwardly curved spines arise, resembling the basal part of a commencing frontal ring.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.05.

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

4. Semantis sigillum, n. sp. (Pl. 92, fig. 1).

Sagittal ring elliptical, with four pairs of stout arborescent spines (two apical and two equatorial pairs), which are irregularly branched and forked, with numerous thin lateral branches. Apex with a short conical trifid vertical horn. Basal ring thorny, with obliquely descending slightly curved bars.

Dimensions.—Height of the sagittal ring 0.12, breadth 0.09.

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

5. Semantis distephanus, n. sp. (Pl. 83, fig. 3).

Sagittal ring thin, semicircular, smaller than the thin basal ring, which exhibits two semicircular gates. Both rings are armed with numerous small spines of equal size, which on the former are arranged in two, on the latter in three regular rows. (The basal rod of the sagittal ring, separating the two basal gates, in fig. 3 is, by mistake, not distinctly enough drawn.)

Dimensions.—Height of the sagittal ring 0.06, breadth 0.08.

Habitat.—Tropical Atlantic, Station 348, surface.

6. Semantis spinescens, Haeckel.

Stephanolithis spinescens, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p.160, Taf. i. fig. 29. Stephanolithis spinescens, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 497, Taf. xxxii. figs. 7a, 7b.

Sagittal ring ovate with four pairs of thin, irregularly branched spines, two apical pairs, one on the straight dorsal rod and one on the curved ventral rod. Basilar rod with a posterior and an anterior forked rod (commencing caudal and sternal foot). Basal ring square, with two lateral spines, and two triangular gates scarcely one-third as broad as the ring-gate. An internal ascending procolumna (rod c₁ in the figure of Bütschli) connects the basal and ventral rods of the sagittal ring.

Dimensions.—Height of the sagittal ring 0.1, breadth 0.07.

Habitat.—Fossil in Barbados.

Genus 408. Semantrum,^[8] n. gen.

Definition.—Semantida with four basal pores (two anterior jugular and two posterior cardinal pores), without typical basal feet.

The genus Semantrum, one of the most important of the Nassellaria, arises from the preceding Semantis by duplication of the two basal gates. Behind the pair of coracal rods there arises from the basilar rod of the sagittal ring a third pair of lateral horizontal branches, the scapular rods. These become connected with the coracal rods on each side, and so produce a second posterior pair of basal pores, the "cardinal gates." These are constantly larger than the anterior "jugular gates." Therefore the vertical ring of Semantrum possesses a horizontal basal ring with four very characteristic gates, enclosed by three pairs of lateral curved and connected branches, and these become transmitted by heredity to the majority of the Nassellaria.

1. Semantrum quadrifore, n. sp. (Pl. 92, fig. 5).

Sagittal ring subcircular or ovate, with three edges and four sagittal forked spines on the odd edge (two dorsal and two ventral spines). Basal ring decagonal, with ten simple or forked spines on the ten corners. Jugular gates tetragonal. Cardinal gates pentagonal.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.07.

Habitat.—Tropical Atlantic, Station 351, surface.

2. Semantrum tetrastoma, n. sp. (Pl. 92, fig. 3).

Sagittal ring semicircular, thorny, without edges. Basal ring tetragonal or nearly cordate, with a small anterior and a large posterior bow-shaped incision; on the lateral edges with numerous irregular thorns. Jugular gates pear-shaped. Cardinal gates nearly kidney-shaped.

Dimensions.—Height of the sagittal ring 0.1 to 0.14, breadth 0.07 to 0.09.

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

3. Semantrum tetrapylum, n. sp.

Sagittal ring elliptical, tuberculate. Basal ring trapezoidal, also with roundish thick rods and small irregular tubercles on the margin. Jugular gates ovate, two-thirds as broad as the triangular cardinal gates.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.05.

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

4. Semantrum mülleri, Haeckel.

Stephanolithis mülleri, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi pp. 499, 539, Taf. xxxii. figs. 8a, 8b, 8c.

Sagittal ring nearly semicircular or obliquely ovate, thorny. Basal ring also nearly semicircular, with two slight sagittal incisions (one anterior and one posterior), on the lateral edges with numerous small thorns. Jugular pores (pair I of Bütschli) pear-shaped. Cardinal pores (pair II of Bütschli) triangular. Sometimes (but not constantly) a pair of cervical bows connects the scapular bars with the subvertical dorsal rod of the sagittal ring.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.06.

Habitat.—Fossil in Barbados.

5. Semantrum sphragisma, n. sp.

Sagittal ring circular, smooth. Basal ring also nearly circular and smooth; its four basal gates of nearly equal size, elliptical or subcircular; the jugular pores scarcely smaller than the cardinal pores. All rods smooth, cylindrical, without edges and thorns.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.07.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms; also fossil in Barbados.

6. Semantrum bütschlii, n. sp.

Sagittal ring triangular, with vertical straight ascending dorsal rod, horizontal straight basilar rod and obliquely ascending, slightly curved ventral rod; all rods nearly cylindrical, with irregular branched thorns and distorted edges. Jugular pores triangular, scarcely half as broad as the large semicircular cardinal pores.

Dimensions.—Height of the sagittal ring 0.11, breadth 0.08.

Habitat.—Fossil in Barbados.

7. Semantrum signarium, n. sp. (Pl. 92, fig. 4).

Sagittal ring obliquely ovate, thorny. Basal ring kidney-shaped or nearly pentagonal, with broad concave dorsal incision and five larger branched spines on the five corners; between them smaller thorns. Jugular gates pear-shaped, scarcely half as broad as the triangular cardinal gates.

Dimensions.—Height of the sagittal ring 0.12, breadth 0.09.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 409. Semantidium,^[9] n. gen.

Definition.—Semantida with six basal pores (two anterior jugular, two middle cardinal, and two posterior cervical pores), without typical basal feet.

The genus Semantidium exhibits a further developmental stage of the basal plate of the Semantida. Whilst this plate in Semantis possesses one pair of basal pores, and in Semantrum two pairs, here in Semantidium it has three pairs. The new third pair is produced on the dorsal edge of the basal plate, which becomes connected with the basal part of the dorsal rod of the sagittal ring by a pair of cervical rods. The middle pair of pores (the cardinal) are always larger than the anterior (jugular) and the posterior (cervical pores). The same form of basal plate is preserved in numerous Spyroidea and Cyrtoidea, as a "cortinar septum with six collar pores," (e.g., Pl. 53, fig. 18).

1. Semantidium hexastoma, n. sp. (Pl. 92, fig. 6).

Sagittal ring ovate, thorny. Basal ring rhombic or nearly square, with four short conical descending spines on the four prominent edges (two sagittal and two lateral); between them numerous smaller irregular thorns. Jugular and cervical gates nearly equal, ovate, half as broad as the triangular cardinal gates between them.

Dimensions.—Height of the sagittal ring 0.14, breadth 0.1.

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

2. Semantidium sexangulum, n. sp.

Sagittal ring ovate, with six pairs of short branched thorns (two apical, two dorsal, and two ventral). Basal ring hexagonal, with three pairs of short branched thorns on the six corners (one sagittal pair, one posterior and one anterior). All six gates of the basal plate triangular, the jugular and cervical a little smaller than the cardinal gates.

Dimensions.—Height of the sagittal ring 0.1, breadth 0.07.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

3. Semantidium haeckelii, Bütschli.

Stephanolithis Haeckelii, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 499, 538, Taf. xxxii. figs. 6a, 6b.

Sagittal ring elliptical, with three pairs of short horizontal branched spines, one apical and two equatorial pairs (one dorsal and one ventral). Basal ring roundish hexagonal, with numerous short thorns on the margin. Jugular pores ovate, about half as broad as the ovate cardinal pores and twice as broad as the small cervical pores.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.06.

Habitat.—Fossil in Barbados.

4. Semantidium signatorium, n. sp. (Pl. 92, fig. 7).

Sagittal ring semicircular, thorny; basal ring pentagonal, with short spines on the margin and five stronger thorny spines on the five corners. Jugular pores ovate, smaller than the triangular cervical pores. Cardinal pores two to three times as large as each of the former, pentagonal.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.12.

Habitat.—North Pacific, Station 341, depth 2300 fathoms.

Genus 410. Clathrocircus,^[10] Haeckel, 1881, Prodromus, p. 447.

Definition.—Semantida with a variable number of pores on the apical and the basal part of the ring, symmetrically arranged, without typical basal feet.

The genus Clathrocircus comprises those Semantida in which the sagittal ring bears not only basal pores (as in the three preceding genera) but also apical pores (on the opposite pole of the main axis), or a variable number of pores along the whole ring. All these pores are symmetrically arranged in pairs. In the simplest form there are only two apical pores opposite to four basal pores, whilst in the highest state of development the whole ring bears two complete circles of pores. At both poles of the transverse axis two large lateral gates remain open. If these become closed by lattice-work, Clathrocircus passes over into Dictyospyris.

1. Clathrocircus hexaporus, n. sp.

Sagittal ring circular, smooth, with three pairs of pores (one apical and two basal). The two apical pores are triangular with two lateral spines, and correspond to the two mitral gates of the Tympanida. The four basal pores form a hexagonal basal plate, with six lateral spines, and correspond to the four basal pores of Semantrum; the two jugular are pear-shaped, and half as broad as the two triangular cardinal pores.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.06.

Habitat.—Cosmopolitan; Atlantic, Pacific, many Stations, surface.

2. Clathrocircus octoporus, n. sp.

Sagittal ring elliptical, smooth, with four pairs of pores (two apical and two basal). The four apical pores are of nearly equal size, subcircular, and form a regular cross around the apical pole. The four basal pores are ovate, and form a quadrangular plate, armed with marginal thorns; the two jugular pores are somewhat smaller than the two cardinal pores.

Dimensions.—Height of the sagittal ring 0.11, breadth 0.08.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

3. Clathrocircus decaporus, n. sp.

Sagittal ring ovate, thorny, with five pairs of pores (two apical and three basal). The four apical pores are roundish and form a cross. The six basal pores are triangular and form a hexagonal plate with thorny margin; the two jugular pores are somewhat larger than the two cervical, and half as broad as the two cardinal pores.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.07.

Habitat.—North Pacific, Station 256, depth 2950 fathoms.

4. Clathrocircus stapedius, n. sp. (Pl. 92, fig. 8).

Sagittal ring ovate, smooth, with six pairs of pores (two apical and four basal). The four apical pores are of nearly equal size and form a quadrangular mitral plate with two large lateral horns. The eight basal pores are of very different size (the four central far larger than the two anterior and the two posterior), and form a hexagonal basal plate, also with two large lateral horns. The four branched lateral horns (two upper and two lower) form together an incomplete frontal ring.

Dimensions.—Height of the sagittal ring 0.1, breadth 0.08.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

5. Clathrocircus dictyospyris, n. sp. (Pl. 92, fig. 9).

Sagittal ring ovate, thorny, with eight pairs of pores. The four apical and the four basal pores are elliptical and far larger than the four dorsal and the four ventral pores. Resembles a Dictyospyris with open lateral gates.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.06.

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

6. Clathrocircus multiforis, n. sp. (Pl. 92, fig. 10).

Sagittal ring circular, smooth, with ten to twelve pairs of roundish pores, forming together a complete lattice-girdle with two parallel circular rows of pores. Four larger of these are the four gates of the basal ring (two jugular and two cardinal pores).

Dimensions.—Diameter of the ring 0.1 to 0.15, breadth 0.03 to 0.05.

Habitat.—Central Pacific, Stations 263 to 274, depth 2350 to 2925 fathoms.

Subfamily 2. Cortiniscida, Haeckel.

Definition.—Semantida with large, typical, regularly disposed basal feet (originally three cortinar feet, one odd caudal and two paired pectoral).

Genus 411. Cortiniscus,^[11] n. gen.

Definition.—Semantida with three typical basal feet (an odd caudal foot and two paired lateral or pectoral feet).

The genus Cortiniscus is of peculiar importance, as the common ancestral form of the Cortiniscida, or those Semantida in which the basal ring is provided with typical, regularly disposed basal feet—three, four, or six. Since these typical basal feet (or "cortinar feet") are preserved in the greater number of all Nassellaria, determining their triradial structure, they possess a great morphological value. Cortiniscus exhibits the same three primary feet as Cortina, from which it differs in the production of two or more basal pores (between the odd caudal and the paired lateral feet).

1. Cortiniscus tripodiscus, n. sp. (Pl. 92, fig. 11).

Sagittal ring ovate, thorny, with three prominent, distorted edges; its dorsal rod nearly straight and vertical, with one or two pairs of short thorns; its ventral rod strongly curved, with three or four pairs of divergent thorns. Basal ring larger than the sagittal ring, with two semicircular gates and obliquely ascending halves, which on the inner and lower edge are smooth, on the outer and upper thorny. Apical horn and the three divergent feet nearly equal, straight, about as long as the sagittal ring, with three thorny edges.

Dimensions.—Height of the sagittal ring 0.1 to 0.12, breadth 0.07 to 0.09.

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

2. Cortiniscus dipylaris, n. sp. (Pl. 92, fig. 13).

Sagittal ring nearly semicircular, with prominent distorted edges and six pairs of small roundish papillate tubercles (three pairs on the straight dorsal, three on the curved ventral rod). Apical horn short and stout, with a tuberculate knob. Basal ring smaller than the sagittal ring with two elliptical gates. Three feet short and stout, irregularly branched like a cauliflower, with numerous short papillate tubercles.

Dimensions.—Height of the sagittal ring 0.11, breadth 0.08.

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

3. Cortiniscus tripylaris, n. sp.

Sagittal ring elliptical, smooth. Apical horn conical, smooth. Basal ring larger than the sagittal ring, with three elliptical gates of equal size; two paired, posterior (jugular pores) between the basal parts of the caudal foot and the two pectoral feet, and an odd, anterior (sternal pore) between the basal parts of the two pectoral feet and a connecting horizontal convex sternal bow.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.06.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

4. Cortiniscus tetrapylaris, n. sp.

Sagittal ring elliptical, with four pairs of short branched thorns, two posterior on the straight dorsal, and two anterior on the curved ventral rod. Basal ring smaller than the sagittal ring, with four triangular gates; the two anterior (jugular pores) a little smaller than the two posterior (cardinal pores). Apical horn and the three divergent feet shorter than the sagittal ring, irregularly branched, with curved, often tuberculate branches.

Dimensions.—Height of the sagittal ring 0.08 to 0.12, breadth 0.06 to 0.1.

Habitat.—Fossil in Barbados.

5. Cortiniscus typicus, n. sp. (Pl. 92, fig. 12).

Sagittal ring ovate, thorny, with three distorted edges; dorsal rod nearly straight and vertical prolonged upwards into a stout thorny apical horn, downwards into the caudal foot. Basal ring smaller than the sagittal ring, with four elliptical or nearly triangular gates; the two anterior (jugular pores) about half as large as the two posterior (cardinal pores). Three feet of equal size, thorny, divergent, straight or slightly curved, about as long as the diameter of the sagittal ring.

Dimensions.—Height of the sagittal ring 0.14 to 0.18, breadth 0.1 to 0.12.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, at various depths.

Genus 412. Stephaniscus,^[12] n. gen.

Definition.—Semantida with four typical basal feet (two sagittal and two lateral or pectoral feet).

The genus Stephaniscus differs from the preceding Cortiniscus in the production of a fourth (sternal) foot, and therefore exhibits the same relation to it that Stephanium among the Stephanida bears to Cortina. It differs from Stephanium, in the production of a basal ring, with pores or gates between the bases of the basal feet. Two of these feet are sagittal (the posterior caudal and the anterior sternal foot), whilst the other two are lateral or pectoral (right and left). The basal lattice-plate exhibits either two pores ("jugular gates") or four pores (two anterior jugular and two posterior cardinal gates).

1. Stephaniscus tetrapodius, n. sp.

Sagittal ring nearly circular, smooth, with a short conical apical horn. Basal ring square, smooth, with two triangular gates. Four feet simple, equal, conical, divergent, about as long as the diameter of the ring.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.07.

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

2. Stephaniscus quadrifurcus, n. sp. (Pl. 92, fig. 14).

Sagittal ring subcircular, thorny with a small thorny apical horn. Basal ring also nearly circular, with two large semicircular gates and a few small thorns. All four feet curved and forked, the fork-branches again ramified, with numerous short curved and pointed branches. The two lateral feet (right and left) are larger and more branched than the two sagittal feet (sternal and caudal foot).

Dimensions.—Height of the sagittal ring 0.12, breadth 0.1.

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

3. Stephaniscus quadrigatus, n. sp. (Pl. 92, fig. 15).

Sagittal ring oblique, ovate, with three prominent thorny edges; its dorsal rod nearly straight and vertical, the ventral rod strongly curved; apex with a small curved horn. Basal ring with a few short thorns and four gates of different size; the two anterior (jugular pores) ovate or nearly triangular, two-thirds as broad as the two posterior subcircular or pentagonal (cardinal pores). All four feet simple, curved, with three edges, the posterior (caudal) foot larger, the anterior (sternal) foot smaller than the two lateral (pectoral) feet.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.07.

Habitat.—Tropical Atlantic, Station 351, surface.

4. Stephaniscus medusinus, n. sp.

Sagittal ring elliptical, thorny, with a larger apical horn. Basal ring nearly square, with short marginal thorns and four large ovate gates of nearly equal size. All four feet of equal size divergent, curved, irregularly branched, with short curved branches.

Dimensions.—Height of the sagittal ring 0.13, breadth 0.09.

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

Genus 413. Semantiscus,^[13] n. gen.

Definition.—Semantida with six typical basal feet (two sagittal, two pectoral, and two tergal feet).

The genus Semantiscus may be the archetype of those Nassellaria which exhibit six typical basal feet, in combination with the sagittal ring. Three of these are the primary feet of Cortina and Cortiniscus, the other three are secondary productions between the former. The basal ring may possess either two, four, or six basal pores.

1. Semantiscus hexapodius, n. sp. (Pl. 92, fig. 16).

Sagittal ring elliptical, with a large branched apical horn. Basal ring small, square, with two small triangular gates (or jugular pores). From its periphery there arise six short and stout cylindrical feet, one very large (caudal) from the posterior corner, two tergal on each side, two opposite (pectoral) from the lateral corners, and one odd sternal from the anterior corner. All six spines bear a bunch of ten to twenty stout pointed conical branches, partly simple, partly forked.

Dimensions.—Height of the sagittal ring 0.12, breadth 0.08.

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

2. Semantiscus hexaspyris, n. sp. (Pl. 92, fig. 18).

Sagittal ring semicircular, broad, latticed, with two pairs of irregular dorsal and two pairs of ventral pores. The dorsal rod is straight and vertical, prolonged upwards into a short serrate apical horn, downwards into a straight linear caudal foot. The ventral rod is curved and prolonged into a similar sternal foot. Basal ring hexagonal, with four ovate gates (two smaller jugular and two larger cardinal pores); its four lateral corners prolonged into four curved thorny lateral feet (two anterior larger pectoral, and two posterior smaller tergal feet). This species may be regarded as a commencing Hexaspyris or Liriospyris.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.06.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Semantiscus hexapylus, n. sp. (Pl. 92, fig. 17).

Sagittal ring ovate, thorny, with a small apical horn. Basal ring with six roundish or nearly triangular gates; the two jugular pores are smaller than the two cardinal and larger than the two cervical pores. The separating bars between these six pores are prolonged into six straight, thorny widely divergent feet; three larger feet (the caudal and the two pectoral) with a pair of apophyses, three smaller between them simple (the sternal and the two tergal feet).

Dimensions.—Height of the sagittal ring 0.13, breadth 0.09.

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

Family L. Coronida, Haeckel.

Triostephida, Haeckel, 1881, Prodromus, p. 445.

Definition.—Stephoidea with two crossed vertical rings, perpendicular one to the other (the primary sagittal and the secondary frontal ring). Usually their common base bears a horizontal basal ring, but a mitral ring (or a horizontal ring at the apex) is never developed.

The family Coronida comprises those Stephoidea in which the primary sagittal ring (of the Stephanida and Semantida) becomes crossed by a second vertical ring, the lateral or frontal ring. Between these two vertical meridian rings, perpendicular to one another, four large apertures remain constantly open, the "lateral" gates. But besides these four constant openings, usually (excepting only in the Zygostephanida) other gates are developed on the common base of the two crossed rings, produced by a third, horizontal, basal ring. These basal gates are the same which we have found already in the Semantida.

The distinction of the Coronida from the other Stephoidea is always easy. In the Stephanida and Semantida, the frontal ring, or the second meridian ring, which we find in all Coronida, is never developed. On the other hand these latter never exhibit the typical "mitral ring," or the second, upper, horizontal ring, which distinguishes the Tympanida.

We distinguish here, among the Coronida, four different subfamilies, which perhaps afterwards may be better separated as families. Of these four groups the Zygostephanida and Acanthodesmida exhibit the nearest relationship to the Stephanida, whilst the Eucoronida and Trissocyclida possess a closer affinity with the Semantida.

The Zygostephanida, constituting the first subfamily, exhibit four large gates only, and differ from all other Coronida in the absence of a basal ring and of basal gates. Therefore the skeleton is entirely composed of two crossed vertical rings, perpendicular to one another; the first is the primary or sagittal ring (inherited from the Stephanida), the second is the new lateral or frontal ring. The four large lateral gates are either quite simple (Zygostephanus) or partly closed by loose and irregular lattice-work (Zygostephanium). The Zygostephanida may be derived directly from the Stephanida by development of lateral branches forming a frontal ring. They commonly possess the same characteristic spines or branches, and the same typical difference between the straight dorsal rod and convex ventral rod of the sagittal ring, which we found in the greater number of Stephanida. The frontal ring is commonly elliptical or kidney-shaped, and much larger than the ovate sagittal ring.

The Acanthodesmida, forming the second subfamily of Coronida, differ from all other members of this family in the possession of a large simple basal gate, surrounded by a simple horizontal basal ring. Only this ring is complete, whilst the two crossed vertical meridian rings (the primary sagittal and the secondary frontal ring) are incomplete, both truncated at the base by the basal ring. Therefore there remain here between the three rings five large gates (recognised previously by Johannes Müller in 1856 in Acanthodesmia): four lateral gates (the same as in the Zygostephanida) and one central basal gate. The latter is always quite simple and serves for the emission of the pseudopodia, arising from the basal pole of the central capsule. The four lateral gates are either quite simple (Coronidium) or partly closed by irregular loose lattice-work (Acanthodesmia). The subfamily Acanthodesmida may be derived either directly from the Stephanida (by development of a central basal gate) or from the Eucoronida (by loss of the basilar part of the sagittal ring).

The Eucoronida, the third subfamily, are the most important group of the Coronida; their numerous species are much more frequent and more widely distributed than those of the other three subfamilies. They may be derived immediately from the Semantida by the development of a lateral or frontal ring. This remains incomplete in the basal part, whilst the two other rings, perpendicular to it (the vertical sagittal ring and the horizontal basal ring), are complete. Therefore the shell constantly exhibits six large open gates between the three rings; four lateral gates (the same as in the Zygostephanida and Acanthodesmida) and two basal gates (inherited from Semantis); the latter correspond to the "jugular pores" of the Spyroidea and Cyrtoidea; they remain constantly simple. The four lateral gates may also remain simple (Eucoronis) or they may become partly closed by irregular loose lattice-work (Plectocoronis). The remarkable genus Podocoronis is distinguished by the development of typical descending basal feet, which are regularly disposed and correspond to the typical "cortinar feet" of the other Nassellaria. There may be developed either two lateral feet (as lower prolongations of the segments of the frontal ring), or three feet (one caudal and two pectoral, as in Cortina and Cortiniscus), or four feet (two sagittal and two lateral, as in Stephanium and Stephaniscus), or six feet (two sagittal, two pectoral, two tergal, as in Semantiscus), sometimes numerous feet (as in Petalospyris and Anthocyrtis, &c.).

The Trissocyclida represent the fourth and last subfamily of Coronida, distinguished from all others in the possession of three complete rings, perpendicular one to another, and of eight large gates separated by them. Two of the three rings are vertical (the primary sagittal and the secondary frontal ring), the third is horizontal (the basal ring). The four upper gates correspond to the four lateral gates of the preceding three subfamilies; the four lower gates are the same as the four basal gates of Semantrum (two primary jugular and two secondary cardinal gates); therefore the Trissocyclida may be derived directly from these Semantida by development of a complete frontal ring. Probably the two jugular gates were originally smaller than the two cardinal, but usually they have become equal. In Tristephanium (the common ancestral form of the Trissocyclida) and in the closely allied Tricyclidium the four basal gates remain smaller than the four lateral gates. But in two other genera, Trissocircus and Trissocyclus, the four lower or basal gates reach the same size as the four upper or lateral gates; therefore all eight gates become equal and the basal ring becomes equatorial. In the most regular species of the latter genera also the three rings become perfectly equal and cannot be any longer distinguished. Here the original bilateral (or dipleuric) fundamental form of the shell passes over into a regular cubic or octahedral form (with three equal, isopolar axes, perpendicular one to another). The eight large gates of the Trissocyclida usually remain simple (Tristephanium, Trissocircus), but sometimes they become partly closed by loose lattice-work (Tricyclidium, Trissocyclus).

The original rings, and the secondary rods or bars, composing the loose framework of the Coronida are either roundish (with circular or elliptical transverse section) or three-edged (with triangular transverse section), rarely quadrangular or provided with distorted edges. The branches or spines arising from them, are either simple or branched, and offer a great variety in number, form, and disposition. The most important forms are those which develop the three typical basal feet of Cortina, e.g., Podocoronis cortina (Pl. 97, fig. 2).

The Central Capsule of the Coronida is the same as in the other Stephoidea (comp. p. 937), and offers all those characteristic peculiarities of "Monopylea" which we have mentioned above in the general description of the Nassellaria (p. 890). Usually it is spherical or ellipsoidal, often violin-shaped or bilobed, with a sagittal constriction. The porochora of its basal pole is in close contact with the base of the sagittal ring.

Synopsis of the Genera of Coronida.

I. Subfamily Zygostephanida. Four lateral gates (no basal gate).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Two meridional rings (sagittal and frontal) complete, perpendicular to one another (no basal ring).	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$	Four lateral gates simple,			414. Zygostephanus.
				Four lateral gates partly latticed,			415. Zygostephanium.
II. Subfamily Acanthodesmida. Five large gates (four lateral and one simple basal).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Two meridional rings (sagittal and frontal) incomplete, both truncated by the complete horizontal basal ring.	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$	Four lateral gates simple,			416. Coronidium.
				Four lateral gates partly latticed,			417. Acanthodesmia.
III. Subfamily Eucoronida. Six large gates (four lateral and two basal).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Two rings (the sagittal meridional ring and the horizontal basal ring) complete, the frontal meridian ring incomplete.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Basal ring without larger descending feet.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Gates simple,	418. Eucoronis.
						Gates partly latticed,	419. Plectocoronis.
				Basal ring with large, regularly disposed, descending feet. Gates simple,			420. Podocoronis.
IV. Subfamily Trissocyclida. Eight large gates (four upper lateral and four lower basal).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Two meridional rings (sagittal and frontal) and the horizontal basal ring complete. All three complete rings perpendicular to one another.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Four upper gates larger than the four lower.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Gates simple,	421. Tristephanium.
						Gates partly latticed,	422. Tricyclidium.
				All eight gates of equal size.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Gates simple,	423. Trissocircus.
						Gates partly latticed,	424. Trissocyclus.

Subfamily 1. Zygostephanida, Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with four large lateral gates, without basal gate. Skeleton composed of two complete vertical rings, perpendicular one to another—the primary sagittal and the secondary frontal ring.

Genus 414. Zygostephanus,^[14] Haeckel, 1862, Monogr. d. Radiol., p. 268.

Definition.—Coronida with four large, simple, lateral gates, without basal gate and lattice-work. Skeleton composed of two simple meridional rings, perpendicular to one another.

The genus Zygostephanus, founded by me in 1862 for the Mediterranean Zygostephanus mülleri, is the simplest and most primitive of all the Coronida, and may therefore be regarded as the common ancestral form of this family. The simple skeleton is composed of two meridional rings only, perpendicular one to another—a sagittal and a frontal ring.

Subgenus 1. Zygostephus, Haeckel, 1881, Prodromus, p. 446.

Definition.—The two vertical rings of nearly equal height, therefore without sagittal constriction.

1. Zygostephanus dissocircus, n. sp. (Pl. 93, fig. 1).

Both rings elliptical, of nearly equal height, smooth, without spines. Frontal ring somewhat longer than the sagittal. No sagittal constriction.

Dimensions.—Height of the rings 0.07, breadth 0.1.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

2. Zygostephanus serratus, n. sp.

Both rings elliptical, of nearly equal height, with a serrate prominent edge on the outer convexity (in the transverse section three-edged). No sagittal constriction.

Dimensions.—Height of the rings 0.08, breadth 0.12.

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

3. Zygostephanus mülleri, Haeckel.

Zygostephanus mülleri, Haeckel, 1862, Monogr. d. Radiol., p. 268, Taf. xii. fig. 2.

Both rings elliptical, of nearly equal height, armed with numerous (about fifty) slender curved spines, as long as the radius of the rings; commonly each ring with twelve pairs of divergent spines. No sagittal constriction.

Dimensions.—Height of the rings 0.06, breadth 0.1.

Habitat.—Mediterranean (Messina), surface.

4. Zygostephanus ramosus, n. sp.

Both rings elliptical, of nearly equal height, armed with numerous branched spines, which are arranged on each ring in two divergent rows; the branches of the spines are curved and partly protect the open gates. No sagittal constriction.

Dimensions.—Height of the rings 0.07, breadth 0.09.

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

Subgenus 2. Zygostephaniscus, Haeckel, 1881, Prodromus, p. 446.

Definition.—The two vertical rings of different heights; the frontal ring higher than the sagittal ring, therefore with a sagittal constriction in the median plane.

5. Zygostephanus reniformis, n. sp.

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, in the latter with a deep sagittal constriction, armed with numerous irregular short spines. Sagittal ring thicker and lower, only two-thirds as high, with four pairs of short divergent spines (two ventral and two dorsal pairs).

Dimensions.—Height of the frontal ring 0.13, breadth 0.2.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

6. Zygostephanus violina, n. sp.

Frontal ring violin-shaped, on the upper and the lower margin concave, with a deep sagittal constriction, armed with numerous irregular spines, which are partly simple, partly branched. Sagittal ring thicker and lower, only half as high, with a few short conical spines at the apical and basal poles.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

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

7. Zygostephanus bicornis, n. sp. (Pl. 93, fig. 2).

Frontal ring violin-shaped, on the upper and the lower margin concave, with a deep sagittal constriction; its two halves pentagonal. Between numerous smaller spines there arise from the frontal ring six groups of larger branched spines, two odd in the corners of the highest points (curved like two horns), two branched pairs on the prominent lateral corners (at right and left), and two pairs in the corners of the lowest points (like four branched basal feet). Sagittal ring only two-thirds as high, with four pairs of irregular spines.

Dimensions.—Height of the frontal ring 0.11, breadth 0.16.

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

Genus 415. Zygostephanium,^[15] Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with four large, partly latticed, lateral gates, without basal gate. Skeleton composed of two meridional rings perpendicular to each other.

The genus Zygostephanium differs from the preceding ancestral genus Zygostephanus in the development of lattice-work along the two crossed rings, produced by their anastomosing branches. Therefore the four large lateral gates between them, which are quite simple, in the preceding genus here become more or less fenestrated.

1. Zygostephanium dizonium, n. sp. (Pl. 93, fig. 3).

Tympaniscus dizonius, Haeckel, 1882, Manuscript.

Both rings elliptical, of nearly equal height, smooth, without spines. Sagittal ring with four pairs of small pores (two apical pairs and two basal pairs). Frontal ring with three pairs of small pores (one pair lateral, one pair above and one pair below).

Dimensions.—Height of the frontal ring 0.08, breadth 0.12.

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

2. Zygostephanium paradictyum, n. sp. (Pl. 93, fig. 4).

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, in the latter with a deep sagittal constriction. Sagittal ring ovate, about two-thirds as high as the frontal ring. Both rings three-edged, armed with numerous short and branched bristle-shaped spines, which anastomose along their three edges and produce two series of irregular polygonal pores.

Dimensions.—Height of the frontal ring 0.08, breadth 0.13.

Habitat.—North Pacific, Station 236, surface.

3. Zygostephanium constrictum, n. sp.

Frontal ring violin-shaped, concave on the upper and lower margins, with a deep sagittal constriction. Sagittal ring ovate, about two-thirds as high as the frontal ring. Both rings covered with numerous branched irregular spines, which partly anastomose along the edges of the rings, and produce small irregular polygonal pores.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

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

Subfamily 2. Acanthodesmida, Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with five large gates (four lateral and one basal). Skeleton composed of three rings, perpendicular one to another, two of which are vertical and incomplete (the primary or lateral, and the secondary or frontal), the third is horizontal and complete (the tertiary or basal ring).

Genus 416. Coronidium,^[16] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with five large simple gates (four lateral and one basal). Skeleton composed of two incomplete meridional rings and one complete basal ring, without lattice-work.

The genus Coronidium and the following, nearly allied Acanthodesmia, form together the peculiar subfamily of Acanthodesmida—not in the wider sense in which I first founded this group (1862, Monogr. d. Radiol., p. 265), but in the restricted sense, which is exactly defined in my Prodromus (1881, p. 445). According to this definition, the shell is composed of three different rings, perpendicular to one another; only one of these is complete, the simple horizontal basal ring; the two others are incomplete and vertical (the primary or sagittal and the secondary or frontal ring). Therefore there remain constantly between the three rings five characteristic large openings or gates; four of these are lateral (between the halves of the two meridional rings), the fifth is basal, enclosed by the horizontal basal ring. The longest known type of this subfamily is Acanthodesmia vinculata, the five characteristic gates of which are clearly distinguished by its discoverer, Johannes Müller ("Das Gehäuse besteht nur aus den Leisten zwischen fünf grossen Lücken"). The Acanthodesmida may be derived from the Eucoronida by reduction of the basilar rod of the sagittal ring. If in Eucoronis this basal rod be lost, Coronidium arises.

1. Coronidium dyostephanus, n. sp. (Pl. 82, fig. 7).

Frontal ring elliptical, with few scattered thorns, twice as broad as high, and three times as broad as the smooth rhombic basal ring. Sagittal ring semicircular, very stout, twice as thick as the two other rings, with short lateral thorns (in the figure seen from the apical pole, which exhibits a four-lobed dimple). Basal gate rhombic.

Dimensions.—Height of the frontal ring 0.08, breadth 0.16.

Habitat.—Central Pacific, Station 263, depth 2650 fathoms.

2. Coronidium diadema, n. sp. (Pl. 82, fig. 8).

Frontal ring kidney-shaped, one and a half times as broad as high, with a slight sagittal constriction. Sagittal ring ovate, smaller, about of the same size as the elliptical basal ring. Rods of all three rings cylindrical, bearing numerous short and stout curved spines, partly simple, partly branched. Four bunches of larger spines on the four corners of the basal ring, and one very large bunch on the apical pole. Basal gate elliptical, one and a half times as broad as long.

Dimensions.—Height of the frontal ring 0.13, breadth 0.18.

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

3. Coronidium cervicorne, n. sp. (Pl. 82, fig. 1).

Frontal ring kidney-shaped, twice as broad as high, one and a half times as broad as the elliptical basal ring, both with a slight sagittal constriction. Sagittal ring ovate. All three rings in the figure seen from the apical pole) with cylindrical rods, armed with numerous stout spines, branched like a deer's antler. Basal gate rather oblong, twice as broad as long.

Dimensions.—Height of the frontal ring 0.08, breadth 0.16.

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

4. Coronidium acacia, n. sp. (Pl. 82, fig. 2).

Frontal ring and sagittal ring nearly circular, of equal size, truncated at the base. Basal ring circular, somewhat smaller. All three rings with prominent edges, bearing bunches of short and straight pointed spines, like those of an Acacia. Basal gate circular.

Dimensions.—Height of the frontal ring 0.12, breadth 0.14.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

Genus 417. Acanthodesmia,^[17] J. Müller, 1856, Monatsber. d. k. preuss.

Akad. d. Wiss. Berlin, p. 485.

Definition.—Coronida with five large, partly latticed gates (four lateral and one basal). Skeleton composed of two incomplete, partly fenestrated meridional rings, and one complete basal ring.

The genus Acanthodesmia, the oldest known form of all Coronida, differs from the preceding Coronidium, its ancestral form, in the development of irregular loose lattice-work along the rings, and therefore bears to it the same relation that Zygostephanium does to Zygostephanus. The first species described by Johannes Müller, Acanthodesmia vinculata ("with five large gates between the bars of the shell") remains the true type of this genus; the second species described by him (Acanthodesmia dumetum) belongs to the Plectanida (Polyplecta).

1. Acanthodesmia vinculata, J. Müller.

Acanthodesmia vinculata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 30, Taf. i. figs. 4-6 (non 7). Lithocircus vinculatus, J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 484.

Frontal ring violin-shaped, one and a half times as broad as high, with a sagittal constriction. Sagittal ring ovate, smaller. The four gates between the two rings are partly fenestrated by a few thin threads, irregularly branched and connecting the two rings. A few short thorns are scattered here and there. Basal gate elliptical.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—Mediterranean (Nice), Atlantic (Canary Islands), surface.

2. Acanthodesmia ceratospyris, n. sp.

Frontal ring violin-shaped, one and a half times as broad as high, with a deep sagittal constriction. Sagittal ring semicircular, half as high as the frontal ring. The four gates between the two rings are partly fenestrated by anastomosing branches of the numerous, irregularly branched spines, which cover all three rings. Basal gate nearly circular, smaller than the sagittal ring.

Dimensions.—Height of the frontal ring 0.08, breadth 0.12.

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

3. Acanthodesmia corona, n. sp. (Pl. 93, fig. 5).

Frontal ring kidney-shaped, nearly twice as broad as high, with a flat sagittal constriction. Sagittal ring semicircular. The four gates between the two rings are partly fenestrated by an arachnoidal network, composed of thin, irregularly branched threads, arising from the rings. The edges of all three rings are armed with irregular thorns. Basal gate circular, larger than the sagittal ring.

Dimensions.—Height of the frontal ring 0.08, breadth 0.14.

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

4. Acanthodesmia mülleri, n. sp.

Frontal ring kidney-shaped with a deep sagittal constriction. Sagittal ring ovate. The four gates between the two rings irregularly fenestrated, with a few large polygonal meshes. Edges of the rings with a few scattered thorns. Basal gate violin-shaped.

Dimensions.—Height of the frontal ring 0.1, breadth 0.16.

Habitat.—Tropical Atlantic, Station 347, surface.

Subfamily 3. Eucoronida, Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with six large gates (four lateral and two basal gates). Skeleton composed of three rings perpendicular to one another, two of which are complete (the vertical sagittal, and the horizontal basal ring); the third is incomplete (the vertical frontal ring).

Genus 418. Eucoronis,^[18] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with six large simple gates (four lateral and two basal). Skeleton composed of two complete rings (the sagittal and basal) and one incomplete (frontal) ring. Basal ring without typical feet.

The genus Eucoronis and the following two nearly allied genera (Plectocoronis and Podocoronis) compose together the important subfamily Eucoronida. In this typical main group of Coronida the shell is constantly composed of three rings and six gates. The vertical sagittal ring and the horizontal basal ring are complete (as in the Semantida); the vertical frontal ring is incomplete. Between these three rings remain six large open gates, the four upper (or lateral) are always much larger than the four lower (or basal gates). Eucoronis may be derived from Semantis by development of the frontal ring.

Subgenus 1. Acrocoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Rings smooth or rough, armed with numerous short spines or thorns.

1. Eucoronis perspicillum, n. sp. (Pl. 82, fig. 6).

Frontal ring elliptical, twice as broad as high, with a slight constriction at the apical pole, armed with three pairs of short conical spines, one apical pair (near the constriction) and two lateral pairs (one upper and one lower pair). Sagittal ring of the same height, half the breadth and double the thickness, also armed with three pairs of spines (one basal, one dorsal, and one ventral pair).

Dimensions.—Height of the frontal ring 0.11, breadth 0.22.

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

2. Eucoronis lævigata, n. sp.

Frontal ring elliptical, smooth, one and a half times as broad as high, without sagittal constriction, with horizontal basal gates. Sagittal ring of the same height and thickness, also elliptical and smooth. No spines on either of the smooth rings.

Dimensions.—Height of the frontal ring 0.1, breadth 0.15.

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

3. Eucoronis nephrospyris, n. sp. (Pl. 82, fig. 5).

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, with a sagittal constriction (often much deeper than in the specimen figured). Sagittal ring ovate, about two-thirds as high as the frontal ring. Rods of both rings without edges, cylindrical, armed with numerous short conical thorns.

Dimensions.—Height of the frontal ring 0.1 to 0.12, breadth 0.15 to 0.18.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, many Stations, surface and at various depths.

4. Eucoronis angulata, n. sp. (Pl. 82, fig. 3).

Frontal ring violin-shaped, twice as broad as high, on the upper and the lower margin concave, with a deep sagittal constriction. Sagittal ring pentagonal, with straight horizontal basal rod, two-thirds as high as the frontal ring. Rods of both rings with sharp prominent edges, bearing numerous short pyramidal spines.

Dimensions.—Height of the frontal ring 0.09, breadth 0.17.

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

Subgenus 2. Lithocoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Rings armed with numerous large, branched or arborescent spines.

5. Eucoronis cervicornis, n. sp.

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, with sagittal constriction. Sagittal ring ovate, two-thirds as high as the frontal ring. Both rings armed with numerous stout spines, irregularly branched like a deer's antler. (Very similar to Coronidium cervicorne, Pl. 82, fig. 1, which I formerly confounded with it, but differing in the complete sagittal ring, which in the latter form is incomplete and has lost its basal part.)

Dimensions.—Height of the frontal ring 0.12, breadth 0.2.

Habitat.—Central Pacific, Station 264, surface.

6. Eucoronis arborescens, n. sp.

Frontal ring kidney-shaped, with a deep sagittal constriction in the concave basal part. Sagittal ring ovate, half as high as the frontal ring. Both rings armed with numerous thin, richly branched and arborescent spines (branches much thinner and more numerous than in the preceding and following species).

Dimensions.—Height of the frontal ring 0.15, breadth 0.25.

Habitat.—Equatorial Atlantic, Station 247, surface.

7. Eucoronis challengeri, n. sp. (Pl. 82, fig. 4).

Lithocoronis challengeri, Haeckel, 1881, Prodromus, p. 445.

Frontal ring violin-shaped, one and a half times as broad as high, with a strong sagittal constriction. Sagittal ring nearly circular, two-thirds as high as the frontal ring. Both rings armed with numerous irregularly branched spines. (The specimen figured, with red central capsule and numerous xanthellæ, was observed living by me at the Canary Islands.)

Dimensions.—Height of the frontal ring 0.1 to 0.12, breadth 0.14 to 0.17.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, surface and at various depths.

Genus 419. Plectocoronis,^[19] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with six large, partly latticed gates (four lateral and two basal). Skeleton composed of two complete rings (the sagittal and basal) and one incomplete (frontal) ring. Basal ring without developed typical feet.

The genus Plectocoronis differs from the preceding Eucoronis, its ancestral form, in the development of loose irregular lattice-work along the two meridional rings, and therefore bears to it the same relation that Acanthodesmia does to Coronidium. If the lattice-work become more complete and close the gates, these Coronida pass over directly into Spyroidea (Zygospyrida).

1. Plectocoronis anacantha, n. sp.

Basal ring and frontal ring elliptical, without sagittal constriction. Sagittal ring ovate. The frontal and sagittal rings are bordered on both edges with an incomplete series of small irregular pores. All three rings smooth, without spines.

Dimensions.—Height of the frontal ring 0.1, breadth 0.16.

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

2. Plectocoronis triacantha, n. sp.

Basal ring and frontal ring nearly circular, without sagittal constriction. Sagittal ring elliptical, prolonged at the apex into an apical horn from which two branched lateral bows descend and unite with the uppermost parts of the frontal ring. Four other small bows descend from the lowermost parts of the latter and unite with the basal ring. From the lateral corners of the basal ring descend two short vertical feet. (May be regarded as derived from Podocoronis toxarium, Pl. 83, Fig. 7, by development of the bows connecting the rings.)

Dimensions.—Height of the frontal ring 0.11, breadth 0.13.

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

3. Plectocoronis pentacantha, n. sp. (Pl. 93, fig. 6).

Basal ring and frontal ring kidney-shaped, with deep sagittal constriction. Sagittal ring ovate, prolonged at the apex into an oblique horn. From the edges of the angular rings delicate threads arise, which anastomose and form irregular arachnoidal meshes, partly closing the four open lateral gates. Two basal gates simple. From the four nodal points of the basal ring there arise four, short diverging feet, comparable to rudimentary cortinar feet (two lateral from the frontal ring and two sagittal from the primary ring, as basal prolongations).

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—Central Pacific, Station 271, surface.

Genus 420. Podocoronis,^[20] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with six large gates (four lateral and two basal). Skeleton composed of two complete rings (the sagittal and basal) and one incomplete (frontal) ring. Basal ring provided with typical, regularly disposed, descending feet (cortinar feet).

The genus Podocoronis differs from the two preceding nearly allied genera in the development of typical radial feet on the basal ring, which by their regular disposition and their general appearance among the Spyroidea and Cyrtoidea obtain great morphological importance. According to the different number and disposition of these basal feet (or "cortinar feet"), the following subgenera may be distinguished (regarded in my Prodromus, 1881, p. 445, as separate genera):—Dipocoronis with two lateral feet, Tripocoronis with three cortinar feet (most important!), Tetracoronis with four crossed feet, Hexacoronis with six radial feet, Stylocoronis with numerous (8 or more feet). These subgenera have important relations to the corresponding genera of Zygospyrida.

Subgenus 1. Dipocoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Basal ring with two descending lateral feet (right and left) as prolongations of the frontal ring.

1. Podocoronis dipodiscus, n. sp.

Basal ring nearly circular, with two conical, straight, parallel descending feet, which are direct lateral prolongations of the subcircular frontal ring, and half as long as it. The ovate sagittal ring bears at the apex a short conical vertical horn. All rings nearly smooth.

Dimensions.—Height of the frontal ring 0.12, breadth 0.14.

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

2. Podocoronis toxarium, n. sp. (Pl. 83, fig. 7).

Basal ring elliptical, with two descending, slightly curved conical feet, lateral prolongations of the subcircular frontal ring. The ovate sagittal ring bears at the apex a cylindrical vertical horn, which is connected by two descending lateral arches (or galear arches) with the uppermost part of the frontal ring.

Dimensions.—Height of the frontal ring 0.1, breadth 0.13.

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

Subgenus 2. Tripocoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Basal ring with three descending feet (one caudal and two pectoral).

3. Podocoronis cortiniscus, n. sp. (Pl. 97, fig. 2).

Basal ring violin-shaped, with three straight divergent thorny feet, about as long as the ovate sagittal ring. The dorsal part of the latter is straight, vertical, and prolonged downwards into the caudal foot, upwards into a stout, thorny, vertical apical horn. The ventral part is semicircular and gives off the lateral branches, forming the kidney-shaped sagittal ring. All the rings and their apophyses are armed with stout thorns. This and the following tripodal species may be directly derived from Cortina.

Dimensions.—Height of the frontal ring 0.1, breadth 0.15.

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

4. Podocoronis tripodiscus, n. sp.

Basal ring kidney-shaped, with three large divergent curved feet, nearly twice as long as the semicircular sagittal ring. The straight dorsal part of the latter is prolonged downwards into the caudal foot, upwards into a large branched apical horn, curved backwards. Differs from the preceding species mainly in the longer curved apophyses and in the larger violin-shaped frontal ring.

Dimensions.—Height of the frontal ring 0.12, breadth 0.2.

Habitat.—North Pacific, Station 238, surface. Fossil in Barbados.

Subgenus 3. Tetracoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Basal ring with four descending feet (two sagittal and two lateral).

5. Podocoronis tetrapodiscus, n. sp.

Basal ring kidney-shaped, with four stout and straight divergent feet, about as long as the sagittal ring; two of them are lateral and arise from the basal corners of the violin-shaped frontal ring (at its junction with the basal ring); two are sagittal, and arise from the basal corners of the semicircular sagittal ring (one posterior caudal and one anterior sternal). The straight dorsal part of the sagittal ring is prolonged upwards into an apical horn. All the rings are thorny.

Dimensions.—Height of the frontal ring 0.15, breadth 0.25.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

Subgenus 4. Hexacoronis, Haeckel

Definition.—Basal ring with six radial descending feet (two sagittal, two pectoral, and two tergal feet).

6. Podocoronis hexapodiscus, n. sp.

Basal ring violin-shaped, with six conical, vertically descending feet, half as long as the sagittal ring; two of them are sagittal (arising from the two basal corners of the sagittal ring, caudal and sternal feet); the other four are lateral, and prolongations of the forked basal parts of the frontal ring, which is inserted on the basal ring with two forked branches; the anterior correspond to the pectoral, the posterior to the tergal feet of Hexaspyris. All the rings are thorny.

Dimensions.—Height of the frontal ring 0.11, breadth 0.17.

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

Subgenus 5. Stylocoronis, Haeckel.

Definition.—Basal ring with numerous (eight to twelve or more) descending feet.

7. Podocoronis petalospyris, n. sp.

Basal ring violin-shaped, with ten to twelve flat lamellar, vertically descending feet, about as long as the ovate sagittal ring. Frontal ring twice as broad as long, elliptical. All rings nearly smooth. Similar to a Petalospyris without lattice-work.

Dimensions.—Height of the frontal ring 0.1, breadth 0.2.

Habitat.—Fossil in Barbados.

8. Podocoronis polypodiscus, n. sp.

Basal ring elliptical, with fifteen to eighteen conical, curved, descending feet, half as long as the ovate sagittal ring. Frontal ring kidney-shaped, one and a half times as broad as long. All the rings armed with short conical spines.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—Central Pacific, Station 273, depth 2350 fathoms.

Subfamily 4. Trissocyclida, Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with eight large gates (four superior lateral and four inferior basal). Skeleton composed of three complete rings, perpendicular to one another; two of which are vertical (the primary or sagittal and the secondary or frontal ring), the third is horizontal (the tertiary or basal ring).

Genus 421. Tristephanium,^[21] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with eight large, simple gates of different sizes; the four upper or lateral gates larger than the four lower or basal gates. Skeleton composed of three simple complete rings, perpendicular to one another.

The genus Tristephanium, and the three following genera derived from it, represent together the interesting subfamily of Trissocyclida (Prodromus, 1881, p. 446). These differ from all other Coronida in the possession of three complete rings, perpendicular to one another. The first of these is the vertical sagittal ring, the second the vertical frontal ring, and the third the horizontal basal ring. Since these three rings lie in the three dimensive planes, they are perpendicular to one another; and between them remain eight large open gates. Originally the four upper or lateral gates (corresponding to those of Zygostephanus) are much larger, the four lower or basal gates (corresponding to those of Semantrum) much smaller; but afterwards the latter may reach the size of the former, so that the basal ring becomes equatorial (in Trissocircus and Trissocyclus). The common ancestral form of the Trissocyclida (Tristephanium) may be derived directly either from Semantrum (by complete development of the frontal ring) or from Eucoronis (by complete development of four basal gates).

Subgenus 1. Triostephus, Haeckel, 1881, Prodromus, p. 445.

Definition.—Sagittal and frontal ring of different size and form.

1. Tristephanium dimensivum, n. sp. (Pl. 93, fig. 9).

Sagittal ring ovate, with a large thorny apical horn, smaller than the two other rings. Frontal ring violin-shaped, with a deep sagittal constriction. Basal ring also violin-shaped, in the sagittal axis constricted. Its four gates (two jugular and two cardinal) of nearly equal size. All three rings angular, armed with scattered, stout, thorny spines, which are larger in the basal half.

Dimensions.—Height of the frontal ring 0.08, breadth 0.12.

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

2. Tristephanium octopyle, n. sp. (Pl. 93, fig. 8).

Sagittal ring ovate, nearly smooth, smaller than the two other rings. Frontal ring kidney-shaped, with a deep basal constriction. Basal ring violin-shaped. The jugular gates about half as large as the cardinal gates. Rods of the rings cylindrical, with few scattered thorns.

Dimensions.—Height of the frontal ring 0.09, breadth 0.14.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Tristephanium hertwigii, Haeckel.

Acanthodesmia hertwigii, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 499, 539, Taf. xxxii. figs. 9a-9c.

Sagittal ring ovate or nearly semicircular; its dorsal rod straight, smooth (fig. 9c, a), its ventral rod (b) curved, thorny. Frontal ring much larger, thorny, violin-shaped, with a slight sagittal constriction. Basal ring smaller than the sagittal ring, thorny, kidney-shaped, with four different gates; the two cardinal pores much larger than the two jugular pores. (The four basal pores are often much larger than in the specimen figured by Bütschli. Also the number, form, and size of the spines is very variable.)

Dimensions.—Height of the frontal ring 0.07 to 0.09, breadth 0.17 to 0.2.

Habitat.—Fossil in Barbados.

Subgenus 2. Tristephaniscus, Haeckel, 1881, Prodromus, p. 445.

Definition.—Sagittal and frontal ring of equal size and form.

4. Tristephanium quadricorne, n. sp. (Pl. 93, fig. 7).

Sagittal and frontal ring of equal size and form, larger than the circular basal ring. From the four corners, in which the latter crosses the two former, arise four strong, divergent spines, branched like a deer's antler. Some smaller spines are scattered on the rings, and a bunch of four spines arises on the apical pole. The four upper gates are triangular, the four lower nearly semicircular, the latter of equal size, half as large as the former.

Dimensions.—Height of the frontal ring 0.13, breadth 0.14.

Habitat.—South Atlantic, Station 342, depth 1445 fathoms.

Genus 422. Tricyclidium,^[22] Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with eight large, partly fenestrated gates; the four upper or lateral gates larger than the four lower or basal gates. Skeleton composed of three latticed complete rings, perpendicular to one another.

The genus Tricyclidium differs from the preceding Tristephanium, its ancestral form, in the development of loose rudimentary lattice-work along the rings, and therefore bears to it the same relation that Plectocoronis does to Eucoronis. It may pass directly over into Dictyospyris.

1. Tricyclidium dictyospyris, n. sp. (Pl. 93, fig. 13).

Sagittal ring ovate, twice as thick as the two other larger rings, which become very thin, thread-like at the lateral junction, and are both slightly violin-shaped, in the middle sagittal plane constricted; the frontal ring larger than the basal. All three rings bear small scattered spines, which are irregularly branched, and by anastomoses of the thread-like branches form small irregular meshes along the rings. The four basal gates are of equal size.

Dimensions.—Height of the frontal ring 0.11, breadth 0.15.

Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.

2. Tricyclidium semantrum, n. sp.

Sagittal ring ovate, smaller than the violin-shaped frontal ring and larger than the elliptical basal ring. All three rings of nearly equal thickness, armed with short irregular branches, which are partly connected, and forming small irregular meshes along the rings. The four basal gates are of different sizes; the two anterior (jugular) gates only half as large as the two posterior (cardinal) gates.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—South Atlantic, Station 348, depth 2450 fathoms.

Genus 423. Trissocircus,^[23] Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with eight large simple gates of equal size. Skeleton composed of three simple complete rings, perpendicular to one another.

The genus Trissocircus, and the following nearly allied Trissocyclus, differ from the two preceding ancestral genera in the remarkable growth of the four basal gates, which reach the size of the lateral gates. Therefore both hemispheres of the shell (the upper or apical and the lower or basal) here become equal and the basal ring becomes equatorial. Sometimes even all three rings attain the same size, so that it is difficult or impossible to distinguish them. In this curious case the Coronida exhibit a striking resemblance to some Sphæroidea.

Subgenus 1. Tricircarium, Haeckel.

Definition.—Sagittal ring smaller than the two other rings, which are both elliptical.

1. Trissocircus lentellipsis, n. sp. (Pl. 93, fig. 10).

All three rings elliptical, of different sizes, smooth, without spines. The sagittal ring is the smallest, but two to three times as thick as the other two rings, which have the larger (transverse) axis common. The smaller (sagittal) axis of the sagittal ring is also the smaller axis of the equatorial ring, whilst the larger (principal) axis of the former is the smaller axis of the frontal ring.

Dimensions.—Height of the frontal ring 0.07, breadth 0.1.

Habitat.—Western Tropical Pacific, Station 224, depth 1850 fathoms.

2. Trissocircus binellipsis, n. sp. (Pl. 83, fig. 6).

Sagittal ring circular, smaller than the other two rings, which are both equal, elliptical, slightly constricted on the poles of the principal and transverse axes. The axis of the circular sagittal ring is the shorter axis of the frontal and equatorial ring, and about half as long as their longer axis. All three rings smooth, without spines.

Dimensions.—Height of the frontal ring 0.08, breadth 0.12.

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

3. Trissocircus octostoma (Pl. 93, fig. 11).

Sagittal ring circular, smaller than the other two rings, which are both equal, elliptical, distinctly constricted at the poles of the principal and transverse axes. The axis of the circular sagittal ring is the shorter axis of the frontal and equatorial ring, about one-third shorter than their longer axis. All three rings armed with short, irregularly branched spines.

Dimensions.—Height of the frontal ring 0.1, breadth 0.12.

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

Subgenus 2. Tricirconium, Haeckel.

Definition.—All three rings equal, circular.

4. Trissocircus octahedrus, n. sp.

All three rings equal, circular, smooth, their rods cylindrical (in the transverse section circular). From each pole of the three equal axes arises a short conical spine; these six spines correspond to the six corners of a regular octahedron.

Dimensions.—Diameter of all three rings 0.08, thickness 0.006.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

5. Trissocircus globus, n. sp. (Pl. 82, fig. 13).

All three rings equal, circular, thorny; their rods prismatic (in the transverse section triangular), with three sharp dentated edges and scattered branched thorns. From each pole of the three equal axes (which correspond to the three axes of a regular octahedron) arises a bunch of larger spines.

Dimensions.—Diameter of all three rings 0.12, thickness 0.01.

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

Genus 424. Trissocyclus,^[24] Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with eight large, partly fenestrated gates of equal size. Skeleton composed of three complete latticed rings, perpendicular to one another.

The genus Trissocyclus differs from its nearly allied ancestral form Trissocircus only in the development of small anastomosing branches along the edges of the rings. The incomplete lattice-work, produced by these anastomoses, partly protects the eight large gates. The three rings are either of equal or of different sizes.

Subgenus 1. Tricyclarium, Haeckel.

Definition.—Sagittal ring circular, smaller than the other two rings, which are both elliptical.

1. Trissocyclus stauroporus, n. sp. (Pl. 83, fig. 5).

Sagittal ring circular, smaller than the other two equal elliptical rings. On each of the six corners (or crossing points of every two rings) are developed four small pores, forming a cross around the poles of the three axes. All three rings smooth, without spines.

Dimensions.—Height of the frontal ring 0.09, breadth 0.13.

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

2. Trissocyclus triaxonius, n. sp.

Sagittal ring circular, smaller than the two other equal elliptical rings. From the edges of all three rings are developed small branches, which by irregular ramification and anastomoses form small irregular meshes along the rings. Similar to Trissocircus octostoma, but with thicker rings; it may be developed from the latter species by connection of the branches which border the rings.

Dimensions.—Height of the frontal ring 0.12, breadth 0.15.

Habitat.—South Pacific, Station 298, depth 2225 fathoms.

Subgenus 2. Tricyclonium, Haeckel.

Definition.—All three rings equal, circular.

3. Trissocyclus sphæridium, n. sp. (Pl. 93, fig. 12).

All three rings equal, circular, thorny; their rods prismatic, three-sided, with three denticulate edges; the teeth of the lateral edges become branched, and form by anastomoses of the branches small irregular meshes, which partly protect the eight large open gates.

Dimensions.—Diameter of the three rings 0.16, thickness 0.012.

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

Family LI. Tympanida, Haeckel.

Parastephida, Haeckel, 1881, Prodromus, p. 446.

Definition.—Stephoidea with two parallel horizontal rings, an upper mitral and a lower basal ring; both connected by complete or incomplete vertical rings, or by parallel vertical columellæ.

The family Tympanida (or Parastephida) differs from the other Stephoidea in the development of two horizontal rings, which lie in horizontal planes and arise from the upper and the lower poles of the primary sagittal ring. Therefore the same formation, which we found in the Semantida on the basal pole only of the main axis, here takes place also on its apical pole. On both poles arise at each side from the sagittal ring two corresponding pairs of curved branches: the lateral ends of the opposite branches (dorsal and ventral branch) become united in the frontal plane and so form two complete horizontal rings. The upper ring, composed of the superior or mitral branches, may be called the mitral ring, the lower ring, formed by the inferior or basal branches, the basal ring. Both rings are commonly of nearly equal size, more rarely of different sizes. Their connection is effected either by the primary (sagittal) ring only, or also by secondary vertical rings, a frontal ring in the lateral plane, or some diagonal meridian rings between the latter and the former. These vertical rings, which connect both horizontal rings in the form of "columellæ," may be either complete or incomplete; in the latter case their apical and basal parts are lost, the dorsal and ventral parts only being preserved.

The Tympanida develop a great variety of different forms, greater than in the three other families of Stephoidea, so that we may distinguish here not less than sixteen genera and seventy-two species. Hitherto only three species were known: Prismatium tripleurum, figured in 1862 in my Monograph, Tympanidium barbadense, figured by Bury in the "fossil Polycystins of Barbados," and Tympaniscus fibula, described in 1875 by Ehrenberg as a Ceratospyris fibula. The number of species in this large and richly developed group will be considerably augmented by further researches. A great many of them exhibit remarkable relations to different Nassellaria. For better survey of the whole family we distinguish here four subfamilies, the first of which (Protympanida) is probably the common ancestral group of the other three. They may have been derived originally either from the Semantida or directly from the Stephanida.

The first subfamily, Protympanida, exhibits a complete primary or vertical sagittal ring, bearing on the upper part a horizontal mitral ring, on the lower part a horizontal basal ring. Therefore the gates of these two parallel rings become bisected by the sagittal ring, each divided into a right and a left half. The sagittal ring itself becomes divided by the two horizontal rings into four parts or rods; two opposite of these are more or less vertical; the dorsal (posterior) and the ventral (anterior) rod; the two other rods are more or less horizontal; the mitral (upper) and the basal (lower) rod.

In Protympanium (Pl. 93, fig. 14), the simplest and most primitive form of Tympanida, the connection of the two horizontal rings is effected only by the dorsal and ventral rods of the sagittal ring forming two parallel more or less vertical "columellæ." In all other Protympanida accessory columellæ are developed between the latter. In the greater number we find two secondary columellæ in the lateral plane, being the lateral segments of an incomplete frontal ring (Acrocubus, Pl. 93, figs. 15-17). Between the latter and the former there are sometimes developed four tertiary columellæ, as segments of two crossed incomplete diagonal rings (Tympanidium, Pl. 94, figs. 1, 18). At other times we find six columellæ; here probably the frontal ring is cleft into halves on each side (Tympaniscus, Pl. 94, figs. 4-7). Some genera are distinguished by the development of an equatorial ring, or a third horizontal ring (between the upper mitral and the lower basal ring); this equatorial ring is either complete (Microcubus Pl. 94, figs. 8-10) or incomplete, developed only laterally (Octotympanum, Pl. 94, figs. 2, 3). The genus Toxarium (Pl. 93, figs. 18-20) is distinguished by the development of accessory pairs of bows in the frontal plane, upper or galear bows and lower or thoracal bows, remarkable as beginnings of the accessory joints, which we distinguish in many Spyroidea and Cyrtoidea as "galea and thorax."

The second subfamily of Tympanida are the Paratympanida, in which the two horizontal rings become closed by lattice-work. The numerous columellæ connecting the two rings are here either divergent (Paratympanum, with two unequal rings, Pl. 94, fig. 14) or parallel and vertical (Lithotympanum, with two equal rings, Pl. 83, fig. 1). The shell of the latter assumes the form of a drum.

A third small subfamily, Dystympanida, is represented by a single genus only, Dystympanium (Pl. 94, figs. 15, 16). Here only the upper or mitral ring is closed by lattice-work, whilst the lower or basal ring exhibits quite a simple opening, a large "basal gate" which has probably arisen by loss of the basilar rod of the sagittal ring. These curious forms exhibit a remarkable resemblance to some Monocyrtida, and also to the Dictyocha (Phæodaria).

The fourth subfamily, the Eutympanida, are distinguished by the simple wide aperture of the two horizontal rings; the upper enclosing a simple "mitral gate," the lower a simple "basal gate." Here probably the two horizontal parts of the sagittal ring (the upper mitral rod and the lower basilar rod) are lost by reduction; its two vertical parts (the dorsal and ventral rods) only remaining and forming the two parallel columellæ, which connect the two horizontal rings (Parastephanus, Pl. 93, fig. 21). In this group also secondary columellæ are commonly developed between the two rings, alternating with the two primary columellæ. Pseudocubus (Pl. 94, figs. 11, 12), resembling an obelisk, exhibits four divergent columellæ; the two sagittal of these are probably the vertical parts of the primary ring, whilst the two lateral are the halves of an incomplete frontal ring. In Lithocubus (Pl. 82, fig. 12) the four columellæ are parallel and vertical, the two rings being equal; the shell here assumes the form of a geometrical cube. Prismatium is distinguished by three parallel columellæ; two of these are probably parts of a frontal ring, whilst the third is the remains of a reduced sagittal ring. In Circotympanum (Pl. 94, fig. 17) and in Lithotympanum (Pl. 82, fig. 11) the number of the columellæ is augmented, there being six to eight or more; in the former they are divergent the two rings being of different sizes), in the latter parallel (the two rings being equal); the fundamental form of the former is a truncated pyramid, of the latter a prism.

Comparing these differences between the four subfamilies of Tympanida, we may suppose that the common ancestral group are the Protympanida, derived from the Semantida by the formation of a mitral ring. If the two horizontal rings become closed by lattice-work, the Paratympanida arise. When the mitral ring only becomes latticed, the basal ring being simple, the Dystympanida originate. Finally, the fourth subfamily, the Eutympanida, may be derived from the Protympanida by the loss of the two horizontal parts of the sagittal ring.

The two horizontal rings (upper mitral and lower basal) and the two vertical rings (primary sagittal and secondary frontal), which thus compose the loose framework of the Tympanida, are rarely smooth, commonly armed with spines or branches, similar to those of the Coronida. The rods or bars are either roundish (with circular transverse section) or angular (commonly with triangular transverse section). The paired branches of the two vertical rings often preserve the characteristic arrangement inherited from the Semantida and Stephanida. The two horizontal rings sometimes exhibit typical apophyses, which recur in the Spyroidea and Cyrtoidea. The mitral ring may possess one odd apical horn and two paired frontal horns (Pl. 93, figs. 16, 17, 19, 23). The basal ring sometimes bears the three typical feet of Cortina (Pl. 93, figs. 16, 22), one odd caudal foot and two paired pectoral feet. Sometimes a fourth (sternal) foot is developed (Pl. 94, fig. 4), at other times only two lateral feet (Pl. 94, figs. 5, 6).

Synopsis of the Genera of Tympanida.

I. Subfamily Protympanida. Two horizontal rings (upper mitral ring and lower basal ring) bisected by the complete sagittal ring.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Two horizontal rings connected by two columellæ.			$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	One complete sagittal ring (no frontal ring),	425. Protympanium.
		Two horizontal rings connected by four columellæ (the halves of the sagittal and the frontal ring).	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right\}\,}$	No equatorial ring.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	No galear and thoracal bows,	426. Acrocubus.
						Galear and thoracal bows,	427. Toxarium.
				An equatorial ring.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Equatorial ring complete,	428. Microcubus.
						Equatorial ring incomplete,	429. Octotympanum.
		Two horizontal rings connected by six or eight columellæ (three or four vertical rings).			$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Six columellæ (three meridional rings),	430. Tympaniscus.
						Eight columellæ (four meridional rings),	431. Tympanidium.
II. Subfamily Paratympanida. Two horizontal rings fenestrated.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Two horizontal rings closed by a lattice-plate, connected by numerous columellæ.			$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Two rings unequal (columellæ divergent),	432. Paratympanum.
						Two rings equal (columellæ parallel),	433. Lithotympanum.
III. Subfamily Dystympanida. Mitral ring fenestrated, basal ring simple.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Two horizontal rings connected by numerous (six to eight or more columellæ).	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$	Mitral ring closed by a lattice-plate, basal ring simple,			434. Dystympanium.
IV. Subfamily Eutympanida. Two horizontal rings (upper mitral ring and lower basal ring) simple. Apical and basal parts of the sagittal ring lost.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Two horizontal rings connected by two or three columellæ (four or five open gates).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Two columellæ (parts of the sagittal ring),			435. Parastephanus.
				Three columellæ (parts of the half sagittal and the frontal ring),			436. Prismatium.
		Two horizontal rings connected by four or more columellæ (six or eight or more open gates).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Four columellæ	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Two rings unequal,	437. Pseudocubus.
						Two rings equal,	438. Lithocubus.
				Six to eight or more columellæ.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Two rings unequal,	439. Circotympanum.
						Two rings equal,	440. Eutympanium.

Subfamily 1. Protympanida, Haeckel.

Definition.—Tympanida with two bisected horizontal rings, connected by the complete vertical sagittal ring. (The upper mitral ring and the lower basal ring become divided by the complete primary or sagittal ring into two horizontal symmetrical gates, two mitral gates on the apical and two basal gates on the basal pole.)

Genus 425. Protympanium,^[25] Haeckel, 1881, Prodromus, p. 447 (sensu emend.).

Definition.—Tympanida with two bisected horizontal rings, connected by two vertical columellæ.

The genus Protympanium, is the most simple form of all Tympanida, and probably the common ancestral form of this family. It arises from Lithocircus by the development of two horizontal rings, perpendicular to the primary sagittal ring. The upper or mitral ring arises by lateral union of two pairs of superior branches, the lower or basal ring by union of two pairs of basal branches of the primary vertical ring.

1. Protympanium primordiale, n. sp.

Mitral and apical ring of equal size, elliptical, smooth, somewhat smaller than the connecting thorny sagittal ring.

Dimensions.—Diameter of the two horizontal rings 0.12, of the sagittal ring 0.15.

Habitat.—Central Pacific, Stations 263 to 274, at various depths.

2. Protympanium amphipodium, n. sp. (Pl. 93, fig. 14).

Mitral and apical rings of equal size, thin, elliptical, smooth, larger than the broad connecting sagittal ring. The latter bears on the apical and on the basal pole two divergent straight spines (lying in the frontal plane), the two apical (or horns) somewhat smaller and not so spiny as the two basal spines (or feet). In the frontal plane there arise from the two horizontal rings on each side two small opposite spines (remnants or beginnings of the lateral frontal ring?).

Dimensions.—Diameter of the two horizontal rings 0.11, of the sagittal ring 0.07.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Protympanium trissocircus, n. sp.

Mitral ring smaller than the basal ring; both rings circular, rough. Sagittal ring in size between the two former. All three rings covered with very small thorns.

Dimensions.—Diameter of the mitral ring 0.08, of the sagittal ring 0.1, of the basal ring 0.12.

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

Genus 426. Acrocubus,^[26] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two bisected horizontal rings, connected by four vertical columellæ. No equatorial ring.

The genus Acrocubus is the most primitive of those remarkable Tympanida, the skeleton of which represents more or less exactly the form of a geometrical cube. A simple complete sagittal ring bears on the superior and on the inferior part two opposite pairs of lateral branches; by union of the convergent branches of each side there arise two horizontal parallel quadrangular rings, which are bisected by the sagittal ring. Therefore the superior ring encloses two triangular mitral gates, the inferior two triangular basal gates. The lateral corners of the two gates of each side are connected by a vertical rod or columella. These two parallel columellæ are the remaining middle parts of the secondary or frontal ring, which is incomplete on the superior and on the inferior face of the body. If the sagittal ring also become incomplete, by the loss of the superior and inferior part (the anterior and posterior only remaining), then Acrocubus is transformed into Lithocubus.

Subgenus 1. Apocubus, Haeckel.

Definition.—Basal ring without descending feet.

1. Acrocubus octopylus, n. sp. (Pl. 82, fig. 9).

Mitral ring somewhat smaller than the basal ring; both rings rhombic, with curved outlines. Sagittal ring elliptical, with six pairs of nodulate protuberances. Four columellæ curved. Nodal points without radial spines.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

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

2. Acrocubus tesseralis, n. sp.

Mitral ring of the same size as the basal ring; both rings square, smooth, with straight outlines. Sagittal ring also square, smooth. Four columellæ straight. Nodal points without radial spines. The shell has the form of a regular geometrical cube, the edges of which are represented by the rings.

Dimensions.—Height of the frontal ring 0.1, breadth 0.11.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

Subgenus 2. Dipocubus, Haeckel.

Definition.—Basal ring with two descending feet.

3. Acrocubus brachiatus, n. sp.

Mitral ring smaller than the basal, both rings square, with thick straight rods. Sagittal ring tuberculate, square, equatorial part thinner. Four columellæ curved, the two lateral ones prolonged downwards into two vertical parallel straight feet of half their length.

Dimensions.—Diameter of the cube 0.12; length of the feet 0.06.

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

4. Acrocubus amphistylus, n. sp.

Mitral and basal rings of nearly equal size, square, with thick curved rods. Sagittal ring elliptical, in the equatorial part thinner. Frontal ring tuberculate. Four columellæ curved, the two lateral ones prolonged downwards into two vertical, tuberculate feet of half their length.

Dimensions.—Diameter of the cube 0.13; length of the feet 0.07.

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

5. Acrocubus arcuatus, n. sp. (Pl. 93, fig. 15).

Mitral and basal rings, as well as the sagittal ring, of the same form as in the preceding nearly allied species. The two lateral columellæ are prolonged not only downwards into two short vertical feet, but also upwards into two curved bows, which are united in a vertical ascending horn, arising from the apical pole of the sagittal ring.

Dimensions.—Diameter of the cube 0.14; total height 0.21.

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

Subgenus 3. Tripocubus, Haeckel.

Definition.—Basal ring with three descending feet (one odd caudal and two paired lateral).

6. Acrocubus lasanum, n. sp.

Mitral ring smaller than the basal, both rings square, with curved rods. Sagittal ring ovate, prolonged upwards into an occipital simple horn, downwards into a caudal foot. Two lateral columellæ prolonged downwards into two pectoral feet. All three feet conical, about as long as the height of the cube.

Dimensions.—Diameter of the cube 0.08; length of the feet 0.07.

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

7. Acrocubus cortina, n. sp. (Pl. 93, fig. 16).

Mitral ring smaller than the basal, both rings elliptical, with curved rods. Sagittal ring ovate, prolonged upwards into an occipital horn, downwards into a caudal foot, as in the preceding species. As in the latter, also, the two lateral columellæ are prolonged downwards into two pectoral feet, but also upwards into two convergent horns, which are united with the occipital horn (commencing the formation of a galea). Rings and feet somewhat thorny.

Dimensions.—Diameter of the cube 0.16; total height 0.2.

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

Subgenus 4. Tetracubus, Haeckel.

Definition.—Basal ring with four descending feet (two sagittal and two lateral).

8. Acrocubus tetrapodius, n. sp.

Mitral and basal rings of the same size, square, with straight rods, sagittal ring also square. The four vertical columellæ are nearly parallel and straight, prolonged upwards into four short conical horns, downwards into four longer conical feet. (The shell has nearly the form of a geometrical cube, the eight corners of which are prolonged into eight vertical conical spines, four smaller ascending and four larger descending.)

Dimensions.—Diameter of the cube 0.09; length of the feet 0.06.

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

9. Acrocubus amphithectus, n. sp. (Pl. 93, fig. 17).

Mitral ring smaller than the basal, both rings elliptical, with curved rods. Four columellæ thorny, also curved, divergent downwards, prolonged upwards into four thorny convergent horns, downwards into four larger branched divergent feet. The two sagittal horns and feet (anterior and posterior) are smaller than the two lateral (right and left); therefore the fundamental form of this species is distinctly amphithect (as in the Ctenophora).

Dimensions.—Breadth of the cube 0.12; total height 0.2.

Habitat.—South Pacific, Station 289, depth 2550 fathoms.

Genus 427. Toxarium,^[27] n. gen.

Definition.—Tympanida with two bisected horizontal rings, connected by four vertical columellæ. In the frontal plane two galear bows project upwards, and two thoracal bows downwards.

The genus Toxarium differs from its ancestral form Acrocubus in the development of two pairs of peculiar bows, placed in the lateral or frontal plane; the upper pair projects above the mitral gates, and may be called the "galear bows," the lower pair projects below the basal gates of the cubical shell, and may be called the "thoracal bows." Both pairs are produced originally by the development of two forked vertical spines, arising in the frontal plane on both poles of the principal axis from the sagittal ring (compare Protympanium amphipodium, Pl. 93, fig. 14). The apical fork-branches become connected with the lateral corners of the mitral gates, the basal branches with those of the basal gates. By development of lattice-work between the bows and the rings some Spyroidea (Amphispyris, &c.) may have arisen. The important genus Toxarium may be divided into three subgenera. In Toxellium all the bows are simple, in Toxonium, all are forked; in Toxidium, the galear bows are simple, the thoracal bows forked.

Subgenus 1. Toxellium, Haeckel.

Definition.—Galear and thoracal bows simple.

1. Toxarium circospyris, n. sp. (Pl. 88, fig. 1).

Galear and thoracal bows simple, of about the same size as the frontal bows between them; all bows armed with scattered simple conical spines. Sagittal constriction deep, half as long as the whole shell. Lateral outlines of the shell nearly parallel.

Dimensions.—Length of the shell 0.16, breadth 0.13.

Habitat.—Central Pacific, Stations 265 to 274, depth 2350 to 2925 fathoms.

2. Toxarium subcirculare, n. sp.

Galear and thoracal bows simple, armed with scattered simple spines of about equal size, smaller than the smooth frontal bows between them. Sagittal constriction very flat. Therefore the frontal perimeter of the shell is nearly circular.

Dimensions.—Length of the shell 0.15, breadth 0.14.

Habitat.—North Atlantic (Antilles), Weber, surface.

3. Toxarium thorax, n. sp. (Pl. 93, fig. 18).

Galear bows simple, smaller than the frontal bows, and these again smaller than the simple thoracal bows; therefore the shell increases in breadth towards the base, and resembles the skeleton of the thorax of one of the higher vertebrates (the bow-pairs corresponding to rib-pairs, the ventral part of the sagittal ring to the sternum, the dorsal part to the vertebral column). Sagittal constriction very deep. All bows are armed with scattered, irregularly branched spines.

Dimensions.—Length of the shell 0.17, breadth 0.2.

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

4. Toxarium constrictum, n. sp.

Galear and thoracal bows simple, of nearly equal size, larger than the frontal bows between them. Therefore the shell is constricted in the equatorial plane. Sagittal constriction also deep. All bows armed with scattered, irregularly branched spines.

Dimensions.—Length of the shell 0.14, breadth 0.12.

Habitat.—North Pacific, Station 236, surface.

Subgenus 2. Toxidium, Haeckel.

Definition.—Galear bows simple, thoracal bows forked.

5. Toxarium cordatum, n. sp. (Pl. 93, fig. 19).

Galear bows simple, thoracal bows forked, both somewhat smaller than frontal bows; all bows armed with scattered simple conical spines, mostly developed at the thoracal bows. Both galear bows are united in a central vertical columella, which arises from the apex of the sagittal ring, and is prolonged into an apical horn. Therefore the sagittal constriction exists only in the basal half of the inversely cordate shell.

Dimensions.—Length of the shell 0.18, breadth 0.16.

Habitat.—South Atlantic, Station 348, depth 2450 fathoms.

6. Toxarium furcatum, n. sp.

Galear bows simple, thoracal bows forked, both somewhat broader than the frontal bows. Shell therefore slightly constricted in the equatorial plane. Sagittal constriction rather deep, equal in the apical and basal parts. All bows armed with scattered spines, which are partly simple, partly forked.

Dimensions.—Length of the shell 0.14, breadth 0.16.

Habitat.—Central Pacific, Station 270, depth 2925 fathoms.

7. Toxarium pedatum, n. sp.

Galear bows simple, smaller than the frontal bows, which are again smaller than the thoracal bows. Therefore the breadth of the shell increases towards the base. Sagittal constriction flat in the apical part, deep in the basal part. All bows armed with small irregularly scattered spines; at the base six larger divergent feet (two lateral, two anterior, and two posterior).

Dimensions.—Length of the shell 0.17, breadth 0.15.

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

Subgenus 3. Toxonium, Haeckel.

Definition.—Galear and thoracal bows forked.

8. Toxarium costatum, n. sp.

Galear and thoracal bows forked, smaller than the frontal bows, all bows thorny, without larger spines. Sagittal constriction on both poles deep. Lateral outlines of the shell nearly parallel.

Dimensions.—Length of the shell 0.15, breadth 0.12.

Habitat.—Indian Ocean, Socotra (Haeckel), surface.

9. Toxarium bifurcum, n. sp. (Pl. 93, fig. 20).

Galear and thoracal bows forked, the former smaller than the frontal bows, the latter larger. Sagittal constriction rather flat on the apical pole, which bears a vertical forked horn, very deep on the basal pole of the primary ring. All bows armed with numerous spines, which are partly simple, partly forked, and mainly developed at the basal part of the thoracal bows.

Dimensions.—Length of the shell 0.2, breadth 0.2.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 428. Microcubus,^[28] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two bisected horizontal rings, connected by four vertical columellæ, which are bisected again by an equatorial ring.

The genus Microcubus is derived from its ancestral form Acrocubus by development of a third horizontal ring, which lies in the equatorial plane, parallel to the upper mitral and the lower basal ring. Whilst these latter are both bisected by the complete vertical sagittal ring, the equatorial ring is complete, and connected at the poles of the sagittal axis with the principal ring, and at the poles of the transverse axis with the frontal ring. Therefore the shell exhibits not eight large gates as in Acrocubus, but twelve, viz., four horizontal gates (two superior mitral and two inferior basal), four upper vertical gates (between the mitral and the equatorial ring), and four lower vertical gates (between the basal and the equatorial ring).

1. Microcubus dodecastoma, n. sp. (Pl. 94, fig. 9).

All twelve gates simple, irregularly ovate or pentagonal. Frontal ring on the sides concave, constricted by the equatorial ring. All rings curved, armed with short irregular thorns. No larger basal spines.

Dimensions.—Length of the shell 0.13, breadth 0.15.

Habitat.—Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.

2. Microcubus pentacircus, n. sp.

All twelve gates simple. Frontal ring on the sides convex, not constricted by the equatorial ring. All rings tuberculate, with irregular roundish knots. No larger basal spines. Similar to the preceding species; but the five rings are much thicker and tuberculate (not thorny); the twelve gates are therefore relatively smaller.

Dimensions.—Length of the shell 0.1, breadth 0.12.

Habitat.—Fossil in Barbados.

3. Microcubus zonarius, n. sp. (Pl. 94, fig. 8).

All twelve gates simple, ovate. Frontal ring on the sides convex, not constricted by the equatorial ring, nearly twice as broad as long. All rings thorny, very thin, except only the broad angular sagittal ring. No larger basal spines.

Dimensions.—Length of the shell 0.08, breadth 0.15.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

4. Microcubus quadrupes, n. sp.

All twelve gates simple, square. Frontal ring square, not constricted by the equatorial ring. All rings smooth, quadrangular. Basal ring with four short vertical conical feet, two of which (right and left) are inferior prolongations of the frontal ring, and arise from the lateral corners of the basal gates; two others are prolongations of the sagittal ring (sternal and caudal), and arise from the medial corners of the basal gates. (The shell is like a small cube with four feet.)

Dimensions.—Length of the shell 0.13, breadth 0.11.

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

5. Microcubus cornutus, n. sp.

Eight gates (two mitral, two basal, and four superior) simple; four inferior gates fenestrated by arachnoidal irregular threads. Frontal ring square, constricted on the sides by the equatorial ring. Basal ring with four short conical vertical feet, as in the preceding species. Sagittal ring with a vertical horn on the apex. All rings with small scattered thorns.

Dimensions.—Length of the shell 0.11, breadth 0.13.

Habitat.—North Pacific, Station 235, surface.

6. Microcubus amphispyris, n. sp. (Pl. 94, fig. 10).

Four gates (two mitral and two basal) simple; eight lateral gates (four superior and four inferior) fenestrated by arachnoidal irregular threads. Frontal ring convex, not constricted by the equatorial ring. Basal ring with six short conical divergent feet (two sagittal and four lateral). Sagittal ring with an apical horn. (Resembles some Spyroidea.)

Dimensions.—Length of the shell 0.08, breadth 0.12.

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

Genus 429. Octotympanum,^[29] n. gen.

Definition.—Tympanida with two bisected horizontal rings converging laterally and connected in the lateral poles of the equatorial plane. Eight large gates.

The genus Octotympanum differs from all other Tympanida in the peculiar connection of the two horizontal rings, which here reach the maximum of their growth, converge towards the equator, and come into direct contact on the poles of the equatorial transverse axis. Therefore the shell appears to be composed of three complete vertical meridian rings, the middle of which (the sagittal ring) is free and simple; the two other (subfrontal) rings are grown together at the lateral poles of the equatorial plane; commonly at these poles there arises (on the right and left) a strong lateral spine, and the base of this (or the crossing point of the two touching horizontal rings) corresponds to the remnants of the shortened frontal ring. The crown-shaped shell exhibits therefore eight large gates; two superior (mitral) and two inferior basal gates, two larger anterior (facial) and two larger posterior (occipital) gates. Seen from the lateral poles only two of the former are visible, and represent the figure of a vertical 8; seen from the sagittal poles, only two of the latter are visible, in the form of a larger horizontal 8. Octotympanum may be derived from Acrocubus by reduction of the lateral frontal ring to a knot (or cross-point), and by maximal extension of the two parallel horizontal rings, which become curved downwards laterally and touch at the lateral poles.

1. Octotympanum octospinum, n. sp.

Mitral gates smaller than the basal gates; upper halves of the two lateral meridional rings smaller than the lower halves. Rings with few scattered thorns; four larger simple spines, nearly horizontal in the equatorial plane; two on the poles of the sagittal axis, two on the poles of the lateral axis. Four other large spines, nearly vertical at the four lowermost basal points of the subfrontal rings.

Dimensions.—Length of the shell 0.09, breadth 0.12.

Habitat.—Central Pacific, Station 273, depth 2350 fathoms.

2. Octotympanum octonarium, n. sp. (Pl. 94, fig. 3).

Mitral gates of the same size as the basal gates; upper and lower halves of the meridional rings of equal size. Rings armed with numerous stout, thorny, simple and forked spines; four very large branched spines in the equatorial plane, nearly horizontal, two on the poles of the sagittal, two on the poles of the transverse axis, the latter curved downwards.

Dimensions.—Length of the shell 0.1, breadth 0.2.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Octotympanum arborescens, n. sp.

Mitral gates smaller than the basal gates, the lower halves of the lateral rings being broader than the upper halves. Rings very spiny, armed with numerous branched spines; ten very large arborescent spines on the lateral rings; two on the poles of the transverse axis, eight on the prominent corners of the diagonal axes (four upper and four lower); sagittal ring thorny.

Dimensions.—Length of the shell 0.8, breadth 0.16.

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

4. Octotympanum cervicorne, n. sp. (Pl. 94, fig. 2).

Mitral and basal gates of equal size, the lower and upper halves of the two crossed lateral rings being nearly equal. Rings armed with numerous branched spines; two very large spines, similar to the antlers of a deer, on the poles of the lateral axis; their branches about half as large as the whole shell. Sagittal ring nearly smooth, with few small thorns on the poles of the main axis.

Dimensions.—Length of the shell 0.16, breadth 0.2.

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

Genus 430. Tympaniscus,^[30] n. gen.

Definition.—Tympanida with two bisected horizontal rings, which are connected by three vertical meridional rings (or six columellæ).

The genus Tympaniscus and the following Tympanidium differ from all preceding Tympanida in the multiplication of the vertical columellæ, which connect the two horizontal bisected rings. Tympaniscus exhibits six columellæ, which may be regarded as halves of three meridional rings. Only one, however, of these is complete (the sagittal ring, which bisects the mitral and the basal ring); the two other meridional rings (placed in diagonal planes) may be regarded as produced by lateral bifurcation of an incomplete frontal ring; this appears to be already foreshadowed in the preceding Octotympanum.

1. Tympaniscus corona, n. sp.

Basal ring larger than the mitral ring, with numerous irregular short spines but without descending feet. Six columellæ strongly curved, in the lower half thicker and thorny; the four lateral much thinner than the two sagittal. Apex of the jointed sagittal ring with a conical horn.

Dimensions.—Length of the shell 0.08, breadth 0.11.

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

2. Tympaniscus bipes, n. sp.

Basal ring of about the same size as the mitral ring, with two lateral descending feet, which are parallel and vertical, simple, without spur, half as long as the sagittal ring. The latter is ovate, twice as long and broad as the two circular frontal rings.

Dimensions.—Breadth of the shell 0.14, length 0.09.

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

3. Tympaniscus dipodiscus, n. sp. (Pl. 94, figs. 5, 6).

Basal ring smaller than the mitral ring, with two lateral descending feet, which are nearly parallel and vertical, obtuse, about as long as the sagittal ring, and which bear on the outside a horizontal spur. Sagittal ring hexagonal, very stout, with a caudal appendix at the base, and with a small sagittal arch, bearing a stout spinulate double knob at the apex. The two subfrontal rings depressed, twice as broad as high, on the outside thorny, connected at each side in the lower half by a double transverse arch.

Dimensions.—Breadth of the shell 0.18, length 0.08 (with spines 0.18).

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

4. Tympaniscus tripodiscus, n. sp. (Pl. 94, fig. 7).

Basal ring of about the same size as the mitral ring, with three large and stout divergent feet (two lateral and one caudal). Sagittal ring stout, broader than the two spiny subsagittal rings; the upper part of the latter bears two ascending arches, which are united with the large apical horn arising from the apex of the sagittal ring. Six columellæ nearly vertical, slightly curved on the outside; their lateral edges armed with numerous simple or forked spines.

Dimensions.—Breadth of the shell 0.1, total length 0.12.

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

5. Tympaniscus quadrupes, n. sp. (Pl. 94, fig. 4).

Basal ring larger than the mitral ring, with four short vertical three-sided pyramidal feet of equal size (two lateral and two sagittal); the feet are three-sided pyramidal, with finely denticulate median edges, and bear at the base a horizontal thorny spur. Sagittal ring at the apex with a very large cross-shaped horn, bearing two horizontal thorny lateral branches; the horn is supported by an anterior and a posterior arch. Six columellæ strongly curved and dentate.

Dimensions.—Breadth of the shell 0.15, length 0.12.

Habitat.—South Pacific, Station 298, depth 2225 fathoms.

6. Tympaniscus fibula, Haeckel.

Ceratospyris fibula, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 3.

Basal ring of about the same size as the mitral ring, with six large conical descending feet; these are prolongations of the six columellæ, nearly of the same length, slightly divergent, and bear at the base a strong horizontal spur. The six columellæ are strongly curved, spiny, and bear above small arches, which are united with the apical horn of the sagittal ring.

Dimensions.—Breadth of the shell 0.09, height 0.05; total height 0.09.

Habitat.—Fossil in Barbados.

7. Tympaniscus dodecaster, n. sp.

Basal ring of the same size as the mitral ring, with six very large and six alternating smaller, slightly divergent, curved feet, about as long an the shell; the larger are the basal prolongations of the six curved, thorny columellæ. Mitral ring spiny, not overgrown with arches, as in the similar preceding species.

Dimensions.—Length of the shell 0.08, breadth 0.12.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

Genus 431. Tympanidium,^[31] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two bisected horizontal rings, which are connected by four vertical meridional rings (or eight columellæ).

The genus Tympanidium differs from all other Protympanida in the development of four vertical rings, placed in four different meridional planes. Only one of these is complete, the primary sagittal ring; the three others are incomplete, inserted on the two horizontal rings, which are formed by the paired mitral and basal branches of the sagittal ring; one of these three lies in the frontal plane, the two others in diagonal meridional planes (between the frontal and sagittal). The shell therefore exhibits twelve large gates, four of which are horizontal (the two superior mitral and the two inferior basal gates); the eight others are vertical, separated by the eight columellæ, or the halves of the four meridional rings. In the subgenus Tympanomma the number of gates amounts to sixteen, the four lateral gates being bisected by an incomplete equatorial ring. The genus Tympanidium may be derived from Acrocubus by development of the two diagonal rings (between the frontal and sagittal).

Subgenus 1. Tympanura, Haeckel.

Definition.—Shell with twelve gates; the four lateral gates simple.

1. Tympanidium foliosum, n. sp. (Pl. 94, fig. 1).

Shell with twelve gates; the four lateral gates simple. Basal gates of the shell larger than the mitral gates. Sagittal ring ovate, much smaller than the three other meridional rings, which are armed with numerous large elegant spines, bearing a lanceolate leaf on a thin pedicle. The sagittal ring bears a bunch of similar spines only at the apex, and on both poles of the sagittal axis (in the equator) a single forked spine, with two thorny branches.

Dimensions.—Length of the shell 0.09 (with spines 0.25), breadth 0.15.

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

2. Tympanidium spinosum, n. sp.

Shell with twelve gates; the four lateral gates simple. Basal and mitral gates of about equal size. Shell similar to that of the preceding species, differing mainly in the different armature; the numerous spines, covering the convex outside of the four vertical rings, are not leaf-shaped, but conical, short, of very variable size, partly simple, partly irregularly branched.

Dimensions.—Length of the shell 0.08 (with spines 0.2), breadth 0.12.

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

Subgenus 2. Tympanomma, Haeckel.

Definition.—Shell with sixteen gates (eight median gates, paired on both sides of the sagittal ring, and eight lateral gates, paired on both sides of the frontal ring). The four lateral gates of the two preceding species (subgenus Tympanura) are bisected in Tympanomma by the lateral parts of an incomplete equatorial ring.

3. Tympanidium binoctonum, n. sp. (Pl. 94, fig. 18).

Shell with sixteen gates; the four lateral gates double, bisected by the lateral parts of an incomplete equatorial ring. Basal gates nearly rectangular, of the same breadth as the pentagonal mitral gates, but twice as long. Equatorial outline of the shell (seen in fig. 18 from the apical pole) octagonal. All rods of the shell thin, smooth.

Dimensions.—Transverse axis of the shell 0.1, sagittal axis 0.06.

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

4. Tympanidium barbadense, Haeckel.

"Hollow cylinder," &c., Bury, 1862, Polycystins of Barbados, pl. xvi. fig. 1.

Shell with sixteen gates; the four lateral gates double, bisected by an incomplete equatorial ring. Basal gates kidney-shaped, of the same breadth as the circular mitral gates, but twice as long. Equatorial outline of the shell elliptical. All rods of the shell thin, smooth.

Dimensions.—Transverse axis of the shell 0.12, sagittal axis 0.08.

Habitat.—Fossil in South Naparima, Trinidad, Barbados.

5. Tympanidium staurocircum, n. sp.

Shell with sixteen gates; the four lateral gates double, bisected by an incomplete equatorial ring. Basal and mitral gates of the shell of about equal size, roundish. Equatorial outline of the shell violin-shaped, with a sagittal constriction. All rods of the shell armed with short irregular spines.

Dimensions.—Transverse axis of the shell 0.12, sagittal axis 0.06.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

Subfamily 2. Paratympanida, Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two fenestrated horizontal rings, which are connected by a variable number of vertical rods or columellæ. The shell therefore becomes more completely latticed than in the other Tympanida, and approaches that of the Spyroidea.

Genus 432. Paratympanum,^[32] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two latticed horizontal rings, connected by numerous descending and diverging columellæ; mitral ring smaller than the basal ring.

The genus Paratympanum and the following nearly allied Lithotympanum form together the small subfamily of Paratympanida, distinguished from the other Tympanida by the fenestration of the two parallel horizontal rings. These rings in Lithotympanum are both equal, whilst in Paratympanum, the basal ring is larger than the mitral ring; therefore the connecting rods or columellæ are in the former parallel and vertical, in the latter divergent and descending. Two opposite ones of these columellæ are parts of the primary sagittal ring, two others are parts of the lateral or frontal ring, whilst the remainder are afterwards intercalated. Paratympanum may be derived from Dystympanium by fenestration of the basal ring.

1. Paratympanum hexastylum, n. sp.

Six divergent columellæ, about as long as the diameter of the hexagonal mitral ring, connect it with the larger hexagonal basal ring. Lattice of the mitral ring hemispherical, with six roundish pores, surrounding a central apical horn. Lattice of the basal ring with one large central pore, surrounded by numerous peripheral pores. Rings and rods smooth, without spines.

Dimensions.—Length of the shell 0.07; breadth of the mitral ring 0.06, of the basal ring 0.09.

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

2. Paratympanum octostylum, n. sp. (Pl. 94, fig. 14).

Eight divergent columellæ, about as long as the diameter of the octagonal mitral ring, connect it with the larger circular basal ring, and bear at each end a divergent, strong, conical spine. Lattice-plate of both rings slightly convex, with numerous subregular circular pores, smooth, without surface spines.

Dimensions.—Breadth of the mitral ring 0.06, of the basal ring 0.09.

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

3. Paratympanum decastylum, n. sp.

Ten divergent columellæ, only half as long as the diameter of the decagonal mitral ring, connect it with the larger circular basal ring. Lattice-plate of the mitral ring nearly hemispherical of the basal ring flat, both with numerous irregular roundish pores and scattered spines. Margin of both rings spiny.

Dimensions.—Breadth of the mitral ring 0.08, of the basal ring 0.1.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 433. Lithotympanum,^[33] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two latticed horizontal rings, connected by numerous parallel and vertical columellæ; mitral and basal rings of equal size.

The genus Lithotympanum has the form of a cylindrical drum, the two fundamental faces of which (the mitral and basal gates) are closed by lattice-work. Both horizontal rings are equal, whilst in the preceding Paratympanum the basal gate is larger than the mitral. It may be derived from the latter by equalisation of these two rings, or directly from Dystympanium by fenestration of the basal ring.

1. Lithotympanum tuberosum, n. sp. (Pl. 83, fig. 1).

Both lattice-plates slightly convex; the mitral plate with six larger marginal pores and one central pore separated by numerous smaller pores; the basal plate with seven large pores only (one central and six peripheral). Surface and margin of the plates uneven, with roundish prominent dimpled tubercles. Both rings connected by ten to twelve simple cylindrical vertical columellæ.

Dimensions.—Length of the shell 0.13, breadth 0.1.

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

2. Lithotympanum spinosum, n. sp.

Both lattice-plates flat, with numerous irregular roundish pores of variable size. Surface thorny. Margin with numerous irregular spines, directed upwards on the mitral, downwards on the basal plate. Both rings connected by eight simple cylindrical vertical columellæ.

Dimensions.—Length of the shell 0.12, breadth 0.08.

Habitat.—Western Tropical Pacific, Station 224, depth 1850 fathoms.

Subfamily 3. Dystympanida, Haeckel.

Definition.—Tympanida with fenestrated mitral ring and simple open basal ring; both horizontal rings connected by numerous vertical or divergent columellæ.

Genus 434. Dystympanium,^[34] n. gen.

Definition.—Tympanida with two horizontal rings, connected by numerous (six to eight or more) divergent columellæ. The upper mitral ring is smaller and latticed, the lower basal ring larger and open.

The genus Dystympanium, representing a peculiar subfamily, differs from all other Tympanida in the different shape of the two parallel horizontal rings. The upper or mitral ring is closed by a lattice-plate (as in Paratympanum), the lower or basal ring is simple and open (as in Eutympanium). Dystympanium may therefore be regarded as an intermediate form between these two genera, and may perhaps be derived from Paratympanum by loss of the lower lattice-plate.

1. Dystympanium dictyocha, n. sp. (Pl. 94, figs. 15, 16).

Basal ring circular, with eighteen to twenty short conical divergent spines. Mitral ring about two-thirds as broad, hexagonal, with six ascending spines on the six corners. The latter are connected with the former by six simple, straight, obliquely descending columellæ, about as long as the diameter of the mitral ring. Mitral lattice-plate slightly convex, with seven roundish pores (six peripheral pores around a central pore).

Dimensions.—Diameter of the basal ring 0.09, mitral ring 0.06; length of the columellæ 0.05.

Habitat.—Tropical Atlantic, Station 338, depth 1990 fathoms.

2. Dystympanium distephanus, n. sp.

Basal ring hexagonal, with six larger spines at the six corners, and numerous smaller ones between them. Mitral ring half as broad as the basal ring, also with six angular spines. The latter are connected with the former by six divergent curved columellæ, about as long as the diameter of the basal ring. Mitral lattice-plate flat, with irregular roundish pores.

Dimensions.—Diameter of the basal ring 0.1, mitral ring 0.05; length of the columellæ 0.09.

Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.

3. Dystympanium medusa, n. sp.

Basal ring circular, with eight larger and numerous smaller divergent spines. Mitral ring two-thirds as broad as the basal ring, octagonal, with eight conical ascending spines on the eight corners. The latter are connected with the former by eight divergent, curved columellæ, as long as the diameter of the mitral ring. Mitral lattice-plate nearly hemispherical, with nine circular pores (eight peripheral pores around one central pore).

Dimensions.—Diameter of the basal ring 0.12, mitral ring 0.08; length of the columellæ 0.09.

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

Subfamily 4. Eutympanida, Haeckel.

Definition.—Tympanida with two simple horizontal rings, which are connected by a variable number of vertical rods or columellæ. Therefore the shell exhibits a large simple mitral gate on the upper, and a large simple basal gate on the lower side; between the two a variable number of lateral gates.

Genus 435. Parastephanus, Haeckel, 1881, Prodromus, p. 446.

Definition.—Tympanida with two simple horizontal rings, connected by two vertical columellæ.

The genus Parastephanus is the simplest among the Eutympanida, and exhibits only two vertical rods or columellæ, which connect the two parallel horizontal rings. One of these latter must be regarded as the mitral or superior ring, the other as the basal or inferior ring; whilst the two parallel columellæ, connecting both, are the remaining vertical parts of the sagittal ring, the upper and lower parts of which are lost. By loss of the latter Parastephanus has probably been derived from Protympanium.

1. Parastephanus circularis, n. sp.

Two horizontal rings smooth, circular, of equal size, connected by two curved smooth columellæ, which are somewhat shorter than the diameter of the rings.

Dimensions.—Diameter of the rings 0.08, length of the columellæ 0.06.

Habitat.—Central Pacific, Station 263, depth 2650 fathoms.

2. Parastephanus quadrispinus, n. sp. (Pl. 93, fig. 21).

Two horizontal rings smooth, elliptical or nearly circular, of equal size, connected by two vertical, slightly curved columellæ, which are about as long as the radius of the rings. Each ring bears two simple lateral spines, which in the mitral ring are curved downwards, in the basal ring upwards, possibly the last remains of a reduced frontal ring.

Dimensions.—Diameter of the rings 0.09, length of the columellæ 0.05.

Habitat.—North Pacific, Station 236, surface.

3. Parastephanus asymmetricus, n. sp. (Pl. 82, fig. 10).

Two horizontal rings thorny, of equal size, irregularly ovate or nearly semicircular, and of somewhat asymmetrical form. The two connecting parallel columellæ are straight, cylindrical, about as long as the diameter of the rings. The peculiar asymmetry in the form of the rings raises the possibility that the two columellæ in this species are the remaining parts of a frontal ring, and that the sagittal ring has altogether disappeared. In this case the convex half of both rings would be the ventral, the straight half the dorsal part.

Dimensions.—Diameter of the rings 0.1, length of the columellæ 0.08.

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

4. Parastephanus dispar, n. sp.

Two horizontal rings elliptical, thorny, of different sizes, the basal ring one and a half times as broad as the mitral ring. The two connecting columellæ are curved, somewhat longer than the diameter of the mitral ring.

Dimensions.—Diameter of the basal ring 0.09, mitral 0.06; length of the columellæ 0.07.

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

Genus 436. Prismatium,^[35] Haeckel, 1862, Monogr. d. Radiol., p. 270.

Definition.—Tympanida with two simple horizontal rings, connected by three vertical columellæ.

The genus Prismatium was hitherto the only known form of the Tympanida, and the only species described in 1862 in my Monograph was Prismatium tripleurum (loc. cit., p. 270, pl. iv. fig. 6). A new species from the Challenger collection (Pl. 93, fig. 22), Prismatium tripodium, explains the true structure of this remarkable genus. The skeleton is composed of nine siliceous rods, corresponding to the edges of a trilateral prism. Six of these are horizontal, and enclose the two parallel triangular horizontal gates, the superior of which is formed by the mitral or coryphal, and the inferior by the basal or cortinar ring. The three other rods are vertical and nearly parallel, and connect (as lateral edges of the prism) the corresponding corners of the two parallel horizontal triangles. Two of these vertical columellæ, together with the two horizontal parallel rods connecting them, represent the complete frontal ring, whilst the third vertical columella is the posterior half of the sagittal ring, the other parts of which are lost.

1. Prismatium tripodium, n. sp. (Pl. 93, fig. 22).

Mitral ring triangular, somewhat smaller than the triangular basal ring, both connected at the corners by three vertical, slightly curved columellæ. From the six corners arise six radial spines of different size and form; the two paired spines of the mitral ring are simple and very small, whilst those of the basal ring are three times as long and bear a lateral branch. The odd spine of the third corner is on both rings larger, and distinguished by some thorns. This difference seems to indicate that these two odd spines correspond to the apical horn and the caudal foot of Cortina, and the columella between them is the rest of the reduced sagittal ring. In this case the quadrangular vertical ring, which is composed of the two paired columellæ and the two connecting horizontal rods, would be probably the frontal ring.

Dimensions.—Length of the shell 0.09, breadth 0.07.

Habitat.—Equatorial Atlantic, Station 347, surface.

2. Prismatium tripleurum, Haeckel.

Prismatium tripleurum, Haeckel, 1862, Monogr. d. Radiol., p. 270, Taf. iv. fig. 6. Acanthodesmia prismatium, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 799.

Mitral and basal rings of equal size, equilateral triangular, both connected at the corners by three vertical equal columellæ. From the six corners arise six short, equal, conical radial spines. The nine rods of the shell correspond to the nine edges of a triangular equilateral prism.

Dimensions.—Length of the shell 0.044, breadth 0.032.

Habitat.—Mediterranean (Messina), surface.

Genus 437. Pseudocubus,^[36] n. gen.

Definition.—Tympanida with two simple horizontal rings of different sizes, connected by four divergent columellæ.

The genus Pseudocubus exhibits the characteristic form of an obelisk, or a truncated four-sided pyramid. The four edges of this obelisk, or the four "columellæ," are the remaining parts of the two incomplete vertical rings; two opposite edges are the dorsal and ventral rod of the sagittal ring; the two alternate edges between these are the lateral rods of the frontal ring. The two horizontal rings, which become connected by the four divergent columellæ, are the smaller mitral ring and the larger basal ring; both are either square or nearly circular.

1. Pseudocubus obeliscus, n. sp. (Pl. 94, fig. 11).

Mitral ring square, with circular gate and two divergent simple spines on each corner. Basal ring twice as broad, square, with four convex sides and one simple spine on each corner. Four columellæ straight. All twelve rods with three smooth edges.

Dimensions.—Breadth of the mitral ring 0.02, of the basal ring 0.05.

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

2. Pseudocubus octostylus, n. sp.

Mitral ring square, with one stout pyramidal spine on each corner. Basal ring twice as broad, square, also with a single strong spine on each corner. Four columellæ straight. All twelve rods with three smooth edges.

Dimensions.—Breadth of the mitral ring 0.04, of the basal ring 0.08.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Pseudocubus hexapylus, n. sp. (Pl. 94, fig. 12).

Mitral ring circular, two-thirds as broad as the subcircular, or nearly square, basal ring; both rings with a simple spine on the two sagittal corners (dorsal and ventral), with a forked or branched larger spine on the two lateral corners (right and left). All twelve rods more or less curved and thorny.

Dimensions.—Breadth of the mitral ring 0.07, of the basal ring 0.1.

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

Genus 438. Lithocubus,^[37] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two simple horizontal rings of equal size, connected by four parallel vertical columellæ.

The genus Lithocubus is very remarkable for the regular cubical form of the skeleton, which is composed of twelve siliceous rods, corresponding to the twelve edges of a cube. Eight of these are horizontal, and enclose the two parallel square horizontal gates, the superior mitral and the inferior basal gate. The four other rods are vertical, parallel, and connect (as lateral edges of the cube) the corresponding corners of the two horizontal squares. Two opposite ones of these four vertical columellæ are the remaining halves of the incomplete sagittal ring; the two alternate are the remaining halves of the incomplete frontal ring. The four lateral gates between these four columellæ are also square or rectangular, and either of the same size as the two horizontal gates, or somewhat larger. Lithocubus may be derived from Acrocubus by reduction of the coryphal and the basal part of the primary sagittal ring, the only remaining parts of which are the anterior and the posterior columellæ.

1. Lithocubus geometricus, n. sp. (Pl. 94, fig. 13).

The twelve rods, corresponding to the edges of the geometrical cube, are straight and smooth; the eight corners provided with a small conical thorn. The shell exhibits six equal square sides, and represents therefore exactly the geometrical form of a cube.

Dimensions.—Diameter of the cube 0.05; thickness of the bars 0.008.

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

2. Lithocubus octacanthus, n. sp.

The twelve rods of the cubical shell are slightly curved, convex, smooth, as in the similar preceding species. It differs from that in the development of eight slender radial spines, arising from the eight corners of the geometrical cube, from two to three times as long as its diameter, and lying opposite in pairs in its diagonals.

Dimensions.—Diameter of the cube 0.06; length of the spines 0.15.

Habitat.—North Atlantic, Canary Islands, surface.

3. Lithocubus vinculatus, Haeckel.

Acanthodesmia vinculata, J. Müller, 1856 (partim), Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. i. fig. 7 (not 4-6).

The twelve rods of the cubical shell are curved and armed with scattered, simple, short spines. The figure 7 of Johannes Müller (loc. cit.) corresponds exactly to the Mediterranean form observed by me at Portofino, and is quite different from his true Acanthodesmia vinculata (loc. cit., figs. 4-6), so that I have no doubt he did observe these two different species (compare above, p. 975).

Dimensions.—Diameter of the cube 0.07; length of the spines 0.02.

Habitat.—Mediterranean (Nice, Portofino).

4. Lithocubus astragalus, n. sp. (Pl. 82, fig. 12).

The twelve rods of the cubical shell are stout and slightly curved, armed with numerous, simple, and irregularly branched spines. Eight larger spines, branched like a deer's antler, arise from the eight corners of the cube.

Dimensions.—Diameter of the cube 0.1 to 0.12; length of the corner spines 0.05 to 0.08.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 439. Circotympanum,^[38] n. gen.

Definition.—Tympanida with two simple different horizontal rings, connected by numerous (six to eight or more) divergent columellæ.

The genus Circotympanum comprises those Tympanida in which two simple horizontal rings of different size (an upper smaller "mitral ring," and a lower larger "basal ring") are connected by a variable number of divergent rods or columellæ (at least six or eight). Circotympanum is probably derived from Tympaniscus or Tympanidium by partial reduction of the sagittal ring, the upper (apical) and lower (basal) part of which is lost. The geometrical fundamental form is a truncated pyramid with six to eight or more edges.

1. Circotympanum hexagonium, n. sp.

Mitral and basal ring hexagonal, the latter twice as broad as the former, each with a simple small spine on the six corners. Six columellæ nearly straight, as long as the radius of the basal ring. All rods with three prominent edges.

Dimensions.—Breadth of the mitral ring 0.06, of the basal ring 0.11.

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

2. Circotympanum octogonium, n. sp. (Pl. 94, fig. 17).

Mitral and basal rings octagonal, the latter one and a half times as broad as the former. Eight columellæ slightly curved, thorny. The mitral ring bears on each corner a short ascending spine, the basal ring a larger, thorny, obliquely descending spine, which has some recurved thorns on the upper edge. All rods more or less thorny.

Dimensions.—Breadth of the mitral ring 0.06, of the basal ring 0.09.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Circotympanum decagonium, n. sp.

Mitral and basal rings circular, the latter nearly twice as broad as the former, both armed with scattered irregular thorns. Ten columellæ smooth, curved.

Dimensions.—Breadth of the mitral ring 0.07, of the basal ring 0.12.

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

Genus 440. Eutympanium,^[39] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two simple equal horizontal rings, connected by numerous (six to eight or more) parallel and vertical columellæ.

The genus Eutympanium contains those Tympanida in which the drum-shaped shell is composed of two simple, parallel and equal horizontal rings, and numerous vertical and parallel rods or columellæ connecting them. The number of the latter is at least six or eight. Two opposite of these must be regarded as remaining vertical parts of the sagittal ring, two others as parts of the frontal ring, whilst the other columellæ (between the former and the latter) are secondary and intercalated. Therefore Eutympanium may be derived from Tympanidium by reduction and loss of the apical and basal parts of the sagittal ring.

1. Eutympanium musicantum, n. sp. (Pl. 83, fig. 2).

Eight parallel and vertical columellæ, simple, straight and smooth. Both horizontal rings equal, circular, each armed with eight to twelve short conical thorns.

Dimensions.—Height of the shell 0.09, breadth 0.07.

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

2. Eutympanium octonarium, n. sp.

Eight vertical columellæ slightly curved, thorny. Both horizontal rings equal, octagonal, each armed with eight large, irregularly-branched spines, which on the mitral ring are directed obliquely upwards, on the basal ring downwards.

Dimensions.—Height of the shell 0.12, breadth 0.1.

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

3. Eutympanium coronarium, n. sp.

Eight thorny columellæ, obliquely descending and curved like a bow, divergent in the upper part, convergent in the lower. Basal ring circular, mitral ring octagonal. Both horizontal rings armed with eight stout thorny spines, which on the mitral ring are smaller and directed obliquely upwards, on the basal ring larger and directed downwards, each with a recurved hook.

Dimensions.—Height of the shell 0.08, breadth 0.06.

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

4. Eutympanium militare, n. sp. (Pl. 82, fig. 11).

Ten parallel and vertical columellæ straight and smooth, cylindrical. Both horizontal rings equal, circular, armed with numerous short conical spines, divergent in all directions. Ten to twenty spines on each ring larger than the others.

Dimensions.—Height of the shell 0.1, breadth, 0.08.

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

5. Eutympanium dodecarium, n. sp.

Twelve vertical columellæ, slightly curved, smooth. Mitral and basal rings circular, both horizontal rings armed with twelve stout, irregularly-branched spines, which are prolongations of the columellæ, and on the mitral ring directed upwards, on the basal ring downwards.

Dimensions.—Height of the shell 0.13, breadth 0.1.

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

1. Archicircus = Primordial ring; ἀρχί, κίρκος.
2. Lithocircus = Ring of silex; λίθος, κίρκος.
3. Zygocircus = Yoked or symmetrical ring; ζυγόν, κίρκος.
4. Dendrocircus = Ring bearing trees; δένδρον, κίρκος.
5. Cortina = Tripod.
6. Stephanium = Small crown or garland; στεφάνιον.
7. Semantis = Signet-ring; σημαντίς.
8. Semantrum = Signet-ring; σήμαντρον.
9. Semantidium = Small signet-ring; σημαντίδιον.
10. Clathrocircus = Lattice-ring; κλῆθρον, κίρκος.
11. Cortiniscus = Small cortina or tripod.
12. Stephaniscus = Small coronet or garland; στεφανίσκος.
13. Semantiscus = Small signet-ring; σημαντίσκος.
14. Zygostephanus = Yoked ring; ζυγόν, στέφανος.
15. Zygostephanium = Small yoked ring; ζυγόν, στεφάνιον.
16. Coronidium = Small crown; κορωνίδιον.
17. Acanthodesmia = Thorn-band; ἄκανθα, δέσμιον.
18. Eucoronis = Good crown; εὖ, κορωνίς.
19. Plectocoronis = Crown with framework; πλεκτός, κορωνίς.
20. Podocoronis = Crown with feet; ποῦς, κορωνίς.
21. Tristephanium = Small crown with three rings; τρίς, στεφάνιον.
22. Tricyclidium = Composed of three small crossed circles; τρίς, κυκλίδιον.
23. Trissocircus = Composed of three crossed circles; τρισσός, κίρκος.
24. Trissocyclus = Composed of three crossed rings; τρισσός, κύκλος.
25. Protympanium = Primordial drum; προτυμπάνιον.
26. Acrocubus = Perfect cube; ἄκρος, κῦβος.
27. Toxarium = Small bow; τοξάριον.
28. Microcubus = Small cube; μικρός, κῦβος.
29. Octotympanum = Drum with eight gates; ὀκτώ, τύμπανον.
30. Tympaniscus = Little drum; τυμπανίσκος.
31. Tympanidium = Small drum; τυμπανίδιον.
32. Paratympanum = Side-drum; παρὰ, τύμπανον.
33. Lithotympanum = Drum of silex; λίθος, τύμπανον.
34. Dystympanium = Hideous drum; δύς, τυμπάνιον.
35. Prismatium = A small prism; πρισμάτιον.
36. Pseudocubus = False cube; ψεῦδος, κῦβος.
37. Lithocubus = Cube of silex; λίθος, κῦβος.
38. Circotympanum = Drum with rings; κίρκος, τύμπανον.
39. Eutympanium = Nice small drum; εὖ, τυμπάνιον.