Report on the Radiolaria/Larcoidea

by Ernst Haeckel

Suborder VI. LARCOIDEA, Haeckel, 1883 (Pls. 9, 10, 49, 50).

Definition.—Spumellaria with lentelliptical central capsule (rarely somewhat modified or allomorphic), with a lentelliptical fenestrated siliceous shell (often modified or allomorphic, and sometimes quite irregular). Growth different in the three unequal dimensive axes, perpendicular one to another. The typical Lentellipsis is characterised by three elliptical dimensive planes of different sizes, perpendicular one to another.

The section Larcoidea, the fourth and last of the Sphærellaria, comprises all those forms of this group in which the fenestrated shell originally is lentelliptical, characterised by different growth in three different axes, perpendicular one to another, all three equal on both poles. The geometrical fundamental form of the shell is therefore a lentellipsis or a triaxial ellipsoid; and this typical form is preserved completely in the majority of Larcoidea in the pure geometrical form of the central capsule.

The three dimensive axes, which determine the typical form of Larcoidea, are commonly differentiated in such a way, that the first, the longitudinal or principal axis, is the longest; both its poles, oral and aboral (or anterior and posterior) are equal. The second, the lateral or transverse axis, is commonly less than the first, greater than the third axis; both its poles are the equal lateral poles (right and left not differentiated). The third dimensive axis, the equatorial or sagittal axis, is commonly the shortest; both its equal poles are the sagittal poles (dorsal and ventral poles not different). The relative size of the three dimensive axes in the human body exhibits similar relations.

The three dimensive planes of the Larcoidea, the sagittal, lateral, and transverse planes, are elliptical, all three of different sizes. The first plane, the median or sagittal plane, is commonly as regards size between the two others; its major axis is the principal, its minor the sagittal axis; it separates the right half of the body from the left. The second plane or lateral plane, is commonly larger than the two others; its major axis the principal, its minor the transverse axis; it separates the dorsal half of the body from the ventral. The third plane, the equatorial or zonal plane, is commonly less than the two others; its major axis the lateral, its minor the sagittal axis; it separates the two principal halves of the body, the oral and aboral halves.

In my Monograph (1862) only very few forms of Larcoidea are described, Tetrapyle and Lithelius (the latter representing a peculiar family, Lithelida). In my Prodromus (1881, pp. 463, 464) I disposed all observed forms of Larcoidea in two different families, the Pylonida and Lithelida. The rich materials of the Challenger collection have since offered an astonishing number of new and interesting forms of this section, so that I can enumerate here fifty-one genera and two hundred and sixty-five species. I dispose them here in four subsections and nine families. Three of these have regular lentelliptical shells, which are not articulate, and without annular constrictions (Larcarida, Larnacida, Pylonida); these form the subsection Pylolarcida. Two other families (Tholonida and Zonarida) are distinguished by annular constrictions, which divide the regular lentelliptical shell into a number of dome-shaped chambers or cupolas; we call these Thololarcida. A third group, Spirolarcida, comprises the Larcoidea with spiral growth; the two families of Lithelida and Streblemida. Finally a fourth group the Sorolarcida is formed by the Larcoidea with irregular shells, also two families, the Phorticida and Soreumida.

The first family of Larcoidea, the Larcarida, contains the most simple forms, beginning with Cenolarcus, a quite simple lentelliptical latticed shell. In Coccolarcus we find already two concentric shells, connected by radial beams, an inner medullary and an outer cortical shell. In Spongolarcus the lentelliptical shell becomes spongy.

The second family, Larnacida, is very similar to the Larcarida, and seems to diverge only by the different mode of connection between the two concentric lentelliptical shells. But in truth this slight difference is of great morphological importance, as it depends on a quite different and peculiar mode of growth. In the foregoing Larcarida (Coccolarcus, &c.), the concentric shells originate in the same manner as in the concentric Prunoidea and Sphæroidea, by radial beams, which arise from the surface of the inner (medullary) shell and become connected by a network to form the outer (cortical) shell. Here, in the Larnacida, a quite similar shell originates in a quite different way, first arrived at in the Pylonida (Trizonium). Both concentric shells become here connected by peculiar lattice girdles, which are developed in the perimeter of the three elliptical dimensive planes. Firstly, on both sides of a simple, spherical, or lentelliptical central chamber, arise two lateral wings (on the poles of the transverse axis), and build around the former a transverse girdle. This is crossed by a larger lateral girdle, the minor axis of which is the major of the former, and perpendicular to both girdles is yet developed a third, the sagittal girdle. If the open fissures or "gates" between these three girdles become closed by network, we obtain Larnacilla, the probable ancestral form of all Larnacida.

Whilst in Larnacilla and Larnacidium this typical trizonal lentelliptical shell constitutes by itself alone the whole skeleton, in the other Larnacida it becomes overgrown by outer envelops, and so becomes enclosed in the interior of the central capsule as a "Larnacilla-shaped medullary shell." If the enclosing external envelops be simply latticed, we get the subfamily Larnacalpida; if they be spongy, we get the Larnacospongida.

The third family, Pylonida, is the most important of all Larcoidea, as not only the largest and most interesting number of species belong to it, but also many other genera (far the greater part of all Larcoidea) may be derived from it. The peculiar character of the Pylonida is determined by the imperfect fenestration of the lentelliptical shell growing in the three dimensive axes in a quite different manner. Each elliptical dimensive plane becomes circumscribed by an elliptical latticed girdle (or fenestrated ring), and between these three girdles (perpendicular one to another) remain wide open fissures of the shell or "gates" (Pylæ). The beginning of the shell-building is the same as in Larnacilla, the most simple form of Larnacida. From a quite simple medullary shell, a spherical, subspherical, ellipsoidal, or lentelliptical central chamber, arise two latticed wings, opposite on the poles of the transverse axis (Monozonium). Both wings are short and wide hollow fenestrated tubes, the axes of which are parallel to the principal axis. Therefore they form together with the central chamber an elliptical transverse girdle. This first girdle becomes crossed by a second lateral girdle; from both poles of the transverse axis arise latticed wings, which unite on the poles of the principal axis, therefore the minor axis of this second larger ring is the major axis of the first smaller ring (Dizonium). Between the two crossed rings remain four wide open gates. Now follows the development of a third sagittal girdle, arising from both poles of the principal axis and overgrowing the four gates. But as this third girdle is larger than the second, four other larger gates arise between the two (in planes perpendicular to the former four gates). Now we have the characteristic and most important trizonal shell (Trizonium), composed of three elliptical lattice-girdles of different size, perpendicular one to another, and enclosing a simple central chamber. If the four gates of this Trizonium become closed by lattice-work, it passes over into Larnacilla, the most important ancestral form of the Larnacida.

This most significant "trizonal shell," either incompletely latticed in Trizonium (with four open gates), or completely latticed by fenestration of the four gates, in Larnacilla, is to be found in far the greater part of all Larcoidea, representing the medullary shell, which is overgrown by an outer cortical shell. In many Larcoidea, in which this "Larnacilla-shell" is absent, it is perhaps lost by phylogenetic reduction, or retrograde metamorphosis.

The same process of triple girdle-building, by which the typical Trizonium-shell or Larnacilla-shell is produced (Haplozonaria), is repeated once or twice in the larger forms of Pylonida. The first system of three girdles (perpendicular one to another) becomes overgrown by a second system of the same formulation in the Diplozonaria, and this becomes overgrown by a third system in the Triplozonaria; in the highest genus of this group, Pylozonium, we find not less than nine girdles (three systems, each of three girdles). Till now only one genus of the whole polymorphous family was well known, Tetrapyle (with five girdles, three of the medullary, two of the cortical shell). If the gates between the girdles remain open, all these forms must be regarded as Pylonida; if the gates afterwards become closed by a network, they pass over into other families.

The fourth family of the Larcoidea is the Tholonida, distinguished by the polythalamous shell being composed of a certain number of roundish or hemispherical chambers (domes or cupolas), which surround a primordial central chamber in quite regular disposition, lying opposite in pairs on the poles of the three dimensive axes. If we imagine that each "wing" (or open half-girdle) of the Pylonida becomes closed by a lattice-work, and so transformed into a hemispherical or roundish cupola, we obtain the characteristic shell of the Tholonida. Indeed every girdle of the former corresponds to a pair of opposite domes of the latter. The axis of each pair of domes is one of the three dimensive axes.

The primordial chamber of the Tholonida (or the central chamber, around which all cupolas are regularly disposed) is either a simple lentelliptical lattice-shell, like Cenolarcus, or it is a trizonal shell (with an enclosed concentric medullary shell), like Larnacilla. As in both cases the building and the disposition of the cupolas around it are quite the same, we can suppose that the whole family of Tholonida may have been derived originally from Larnacilla (or Trizonium), and that the Cenotholida (with a simple central chamber) are sprung from the Coccotholida (with a Larnacilla-shaped central chamber) by reduction and loss of the original medullary shell.

The family Tholonida can be divided into three subfamilies according to the disposition of the cupola-pairs in one, two, or three dimensive axes. In the Cubotholida lie two cupolas on the poles of the transverse axis of the central chamber (corresponding to Amphipyle); in the Staurotholida we find four cupolas crosswise disposed, on the poles of the transverse and principal axes (corresponding to Tetrapyle); in the Cubotholida are at least six cupolas, on the poles of all three dimensive axes (corresponding to Tholonium). In all three cases the number of cupolas may be augmented by the secondary apposition of other chambers or domes in the same disposition. Sometimes also the whole cortical shell becomes enclosed by an external veil or mantle of delicate network. The lentelliptical (or often nearly cubical) central chamber becomes often reduced, so that its sides are incompletely latticed or widely opened; in some Cubotholida only the twelve edges of the eight cornered cubical central chamber remain; its six sides are quite open and only over-vaulted by the six hemispherical cupolas. From the opposite points of the latter (in the deep annular constrictions between them) often arise radial spines, and these lie commonly in diagonal planes, separating the dome-pairs.

A similar dome-building or a composition of the polythalamous shell by pairs of cupolas we find also in the next (fifth) family, the Zonarida. But here the true cause of the peculiar dome-structure is quite different, not an apposition of new chambers, but the constriction of a cortical shell-like Larnacalpis by two or more constrictions. These constrictions lie in dimensive planes (or in planes parallel to these), and therefore the cupolas are (all or partly) in diagonal planes, a condition quite opposite to that found in the Tholonida. One of the annular constrictions is constantly in the sagittal plane (separating the right and left halves of the shell). The number of the constrictions in the few genera is two, three, and four, and therefore the number of the cupolas four, six, or eight. As this cortical shell constantly encloses a trizonal medullary shell (or Larnacilla-shell), we cannot doubt that the Zonarida must be derived from the Larnacida.

Whilst in all the foregoing five families of Larcoidea the shell-form is regular and their geometrical fundamental form is a lentellipsis (or a triaxial ellipsoid, with three unequal isopolar dimensive axes), in the four remaining families of this suborder the shell becomes bilateral or irregular (with the poles of the axes unequal). In two of these families (Lithelida and Streblemida) the growth of the shell becomes spiral, in the last two families (Soreumida and Phorticida) quite irregular. But as in all four families we encounter the typical trizonal medullary shell (or Larnacilla-shell), we are convinced that they must be derived (wholly or partially) from the Larnacida.

The Lithelida (the sixth family) are Larcoidea with spiral growth and bilateral form (like Nautilus); therefore the spiral line lies in one plane and this spiral plane divides the whole shell into two symmetrical halves (right and left). The axis of the spiral (around which the shell winds) is a straight line, one of the three dimensive axes. In the greater part of Lithelida (in the Larcospirida) the primordial of central chamber of the polythalamous shell is a trizonal medullary shell or Larnacilla-shell, and the growth of the first spiral turning begins as the development of the first (transverse) cortical girdle of Amphipyle; but as one wing (or lateral half) of this girdle grows more rapidly than the other, it overgrows the latter and begins the spiral winding; if the other wing follow and overgrow the first, the spiral becomes double. Each of the three dimensive girdles (of the Pylonida) may begin the spiral winding. There can be no doubt that all these Lithelida (the Larcospirida) must be derived from the Pylonida, by unequal growth of the two halves of one girdle. Perhaps from these may also derived the other part of this family, the Spiremida (Spirema and Lithelius); in these the primordial chamber of the spiral shell is simple, and may be derived by reduction of the original Larnacilla-shell. But it is also possible that the Spiremida proceed directly from the Larcarida, and that their ancestors did not possess a Larnacilla-shell.

The Streblemida (the seventh family) are Larcoidea with spiral growth and asymmetrical form of the polythalamous shell (like Helix or Turrilites); therefore the spiral line is twisted like a winding stair, and the spiral face is curved and divides the shell into two unequal halves. The Streblemida have the same likeness and relation to the turbinoid Foraminifera (Rotalia, Globigerina, &c.) as the Lithelida to the nautiloid Foraminifera (Polystomella, Nummulina, &c.). As in these calcareous Rhizopods also the peculiar growth of the siliceous Streblemida begins from a primordial chamber to which a variable number of roundish chambers (of increasing size) is apposed. But the building of these chambers and of their septa is by no means so regular and complete as in the greater number of turbinoid Foraminifera. As in a part of this family the primordial chamber is Larnacilla-shell, these also may be derived from the Larnacida, but the other part (with simple central chamber) is perhaps produced directly from the Larcarida.

The eighth family, Soreumida, is perhaps derived from the Streblemida by the loss of the spiral growth. The polythalamous shell is similar to the latter, but the chambers are aggregated without any order, like the Acervulinida among the Foraminifera. In some cases also here the primordial chamber is a trizonal Larnacilla-shell, in other cases it is a simple, subspherical or lentelliptical shell.

The last family, the Phorticida, is formed of irregular Larcoidea, in which a lentelliptical trizonal Larnacilla-shell (as an inner medullary shell) is enveloped by an irregular, latticed, or spongy cortical shell. They can be regarded as abnormalities or irregular deformities of Larnacida or Pylonida.

The central capsule of the Larcoidea is originally lentelliptical and preserves this form, the "triaxial ellipsoid," in the greater number of genera. In some groups it follows the prevalent growth of the shell in the direction of one of the three dimensive axes, and becomes prolonged in this way. In many chambered forms (particularly Tholonida and Zonarida) the growing central capsule gets constricted, corresponding to the constrictions of the shell. In the Soreumida and Phorticida its form often becomes irregular. But in general for the greater number of Larcoidea the lentelliptical form of their central capsule is quite characteristic.

Synopsis of the Families of Larcoidea.

Larcoidea with a regular or symmetrical shell, the growth of which is determined by the three dimensive axes. (Both poles of each axis are equal.)	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Cortical shell completely latticed, without external gates (or interzonal fissures), without annular constrictions and domes.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Medullary shell absent or simple (spherical or lentelliptical),	1. Larcarida.
				Medullary shell trizonal or Larnacilla-shaped (composed of three dimensive girdles),	2. Larnacida.
		Cortical shell incompletely latticed, with two to four or more symmetrically disposed gates or fissures remaining between latticed dimensive girdles,			3. Pylonida.
		Cortical shell completely latticed, without external gates (or interzonal fissures), with two or more annular constrictions, which separate three to six or more dome-shaped protuberances.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Constrictions of the cortical shell in diagonal planes; domes in dimensive axes,	4. Tholonida.
				Constrictions of the cortical shell in dimensive planes; domes in diagonal axes,	5. Zonarida.
Larcoidea with a symmetrical or irregular shell, either with spiral growth or with quite irregular growth. (Both poles of one axis are different.)	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Cortical shell with spiral growth.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Spiral cortical shell bilateral (with plane spiral),	6. Lithelida.
				Spiral cortical shell asymmetrical (with ascending spiral),	7. Streblemida.
		Cortical shell with quite irregular growth.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Cortical shell simple, with one single chamber,	8. Phorticida.
				Cortical shell composed of a number of heaped up or aggregated chambers,	9. Soreumida.

Family XXIV. Larcarida, Haeckel, 1883 (Pl. 50, figs. 1, 2).

Definition.—Larcoidea with a regular, completely latticed, lentelliptical cortical shell, without open gates and annular constrictions; medullary shell absent or simple (not trizonal), connected with the cortical shell by radial beams.

The family Larcarida opens the long series of Larcoidea as the most simple group of this suborder. It commences with Cenolarcus, a quite simple lentelliptical latticed shell, which is characterised by three unequal isopolar dimensive axes, perpendicular one to another. The major of these three axes is the longitudinal or principal, the middle is the lateral or transverse, and the minor is the equatorial or sagittal axis (as in the human body). Among the three dimensive planes, which are determined by pairs of these axes, the lateral plane is the largest (halved by the crossed principal and lateral axes). The intermediate is the sagittal plane or median plane (halved by the crossed principal and sagittal axes). The smallest is the equatorial plane or transverse plane (halved by the crossed lateral and sagittal axes). Therefore the shell has all the characters of the true Lentellipsis or of the "triaxial ellipsoid," and its axes agree with the three axes of the "rhombic crystalline system."

In the three subfamilies of Larcarida this lentelliptical shell assumes a different shape: in the Cenolarcida it remains simple, in the Spongolarcida it becomes spongy (sometimes quite filled out with a spongy framework), in the Coccolarcida it is composed of two or more concentric lentelliptical shells (at least an inner medullary and one outer cortical shell). These shells are simply connected by radial beams, and not, as in the Larnacida, by latticed wings (or half girdles).

The network of the Larcarida shell is sometimes regular, commonly irregular (as in the greater number of Larcoidea). The surface of the shell is sometimes smooth or thorny, at other times covered with radial spines. These are often symmetrically disposed, either on the poles of the dimensive axes or in crossed diagonal planes.

The central capsule is a true "lentellipsis" in a geometrical sense; it is halved by three elliptical dimensive planes of different sizes, perpendicular one to another. In the Cenolarcida the central capsule lies freely inside the simple (cortical) shell, only separated from it by the jelly-mantle. In the Coccolarcida it contains the medullary shell, and is enclosed by the simple or double cortical shell, perforated by the radial beams connecting the two shells. The spongy shell of the Spongolarcida exhibits a different relation to the central capsule: in Spongolarcus the latter lies freely in the internal cavity of the spongy shell; in Stypolarcus, where this cavity is quite filled with a spongy network, the central capsule also contains a part of it.

The morphological and phylogenetic relations of the Larcarida to the other families of Spumellaria admit of a different explanation. As this family contains the most simple forms of all Larcoidea, we can regard the Cenolarcus as the common ancestral form of this group, having originated from Actilarcus (or the lentelliptical Actissa) by the building of a simple lentelliptical lattice-shell. But it is also possible that a part of the Larcarida (or all?) descend from Larnacida by reduction or loss of the original Larnacilla-shell (compare Cenolarcus triaxonius, p. 607).

Synopsis of the Genera of the Larcarida.

III. Subfamily Cenolarcida. Shell simple, latticed (lentelliptical cortical shell).	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Without radial spines,	266. Cenolarcus.
		With radial spines,	267. Larcarium.
III. Subfamily Coccolarcida. Shell composed of two or more concentric latticed shells (inner medullary and outer cortical).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Without radial spines,	268. Coccolarcus.
		With radial spines,	269. Larcidium.
III. Subfamily Spongolarcida. Shell spongy, partly or whole composed of a spongy framework.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	With an internal cavity,	270. Spongolarcus.
		Without an internal cavity,	271. Stypolarcus.

Subfamily 1. Cenolarcida, Haeckel.

Definition.—Larcarida with a simple, lentelliptical latticed shell (cortical shell without a medullary shell).

Genus 266. Cenolarcus,^[1] n. gen.

Definition.—Larcarida with a simple, lentelliptical latticed shell, without a medullary shell, without radial spines.

The genus Cenolarcus begins the group of Larcoidea as the most simple form of this suborder. It corresponds to Cenosphæra among the Sphæroidea, to Cenodiscus among the Discoidea, to Cenellipsis among the Prunoidea. The simple latticed shell is distinguished from that of the three other genera by its typical lentelliptical form, a triaxial ellipsoid with three dimensive axes of unequal length. Probably Cenolarcus is the original ancestral form of the Larcoidea, derived from Actilarcus (the lentelliptical Actissa) by the formation of a simple fenestrated shell around the lentelliptical central capsule. But possibly also some species of Cenolarcus may be derived from Coccolarcus or Larnacilla by reduction and loss of the medullary shell (compare Cenolarcus triaxonius, n. sp.).

1. Cenolarcus primordialis, n. sp. (Pl. 50, figs. 7, 7a, 7b).

Network of the shell regular, with circular, hexagonally framed pores, twice as broad as the elevated bars; about ten pores on the half meridian, eight on the half equator. Surface a little rough. Proportion of the three dimensive axes = 2 : 2.5 : 3.

Dimensions.—Principal axis (or length) 0.12, transverse axis (or breadth) 0.1, sagittal axis (or thickness) 0.08; pores 0.01, bars 0.005.

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

2. Cenolarcus dimensivus, n. sp.

Network of the shell regular, with circular pores (without hexagonal frames), three times as broad as the thin bars; about twelve pores on the half meridian, nine on the half equator. Surface thorny. Proportion of the three dimensive axes = 3 : 4 : 5.

Dimensions.—Principal axis 0.15, transverse axis 0.12, sagittal axis 0.09; pores 0.012, bars 0.004.

Habitat.—North Pacific, Station 244, surface.

3. Cenolarcus triaxonius, n. sp.

Network of the shell regular, with circular, hexagonally framed pores, four times as broad as the thin bars; about twelve pores on the half meridian, nine on the equator. Surface smooth. From the inner surface of the shell arise six very thin radial beams, opposite in pairs in the three dimensive axes; all six beams end freely in a little knob, at an equal distance from the centre; therefore this remarkable species seems to have lost a medullary shell (descending from Coccolarcus or Larnacilla?). Proportion of the three dimensive axes = 2 : 2.5 : 3.

Dimensions.—Principal axis 0.13, transverse axis 0.11, sagittal axis 0.09; pores 0.012, bars 0.03.

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

4. Cenolarcus lentellipticus, n. sp.

Network of the shell regular, with circular pores of the same breadth as the thick bars; about eighteen pores on the half meridian, fourteen on the half equator. Surface smooth. Proportion of the three dimensive axes = 2 : 3 : 4.

Dimensions.—Principal axis 0.16, transverse axis 0.12, sagittal axis 0.08; pores and bars 0.004.

Habitat.—Western Tropical Pacific, Station 224, surface.

5. Cenolarcus minimus, n. sp.

Network of the shell subregular, with very small circular pores of the same breadth as the bars; only four pores on the half meridian, three on the half equator. Surface smooth. Proportion of the three dimensive axes = 3 : 4 : 5.

Dimensions.—Principal axis 0.05, transverse 0.04, sagittal axis 0.03; pores and bars 0.006.

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

Genus 267. Larcarium,^[2] n. gen.

Definition.—Larcarida with a simple, lentelliptical latticed shell, without a medullary shell; surface covered with radial spines.

The genus Larcarium differs from Cenolarcus only in the possession of radial spines on the surface of the simple fenestrated lentelliptical shell. These spines are commonly disposed symmetrically, opposite in pairs, either on the poles of the three dimensive axes, or on the poles of certain diagonal axes. Larcarium differs from the similar genera Larcidium, Larnacidium, and Larnacantha by the absence of any medullary shell.

1. Larcarium amphistylum, n. sp.

Shell thorny, with two large conical spines, opposite on both poles of the principal axis, somewhat longer than it. Network of the shell regular, with circular, hexagonally framed pores, twice as broad as the bars; about twelve pores on the half meridian, ten on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5.

Dimensions.—Principal axis (or length) 0.15, transverse axis (or breadth) 0.12, sagittal axis (or thickness) 0.09; pores 0.01, bars 0.005.

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

2. Larcarium staurostylum, n. sp.

Shell smooth, with four short three-sided pyramidal spines of equal length, opposite in pairs on the poles of the principal and lateral axes. Network of the shell regular, with circular pores of the same breadth as the bars; about eight pores on the half meridian, six on the half equator. Proportion of the three dimensive axes = 2 : 2.5 : 3.

Dimensions.—Length of the shell 0.12, breadth 0.1, thickness 0.08; pores and bars 0.006.

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

3. Larcarium hexastylum, n. sp.

Shell smooth, with six short conical spines of equal length (= the shortest axis of the shell), opposite in pairs on the poles of the three dimensive axes. Network of the shell subregular, with circular pores three times as broad as the bars; about eleven pores on the half meridian, nine on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5.

Dimensions.—Length of the shell 0.1, breadth 0.08, thickness 0.06, pores 0.006; bars 0.002.

Habitat.—North Pacific, Station 244, surface.

4. Larcarium axostylum, n. sp.

Shell thorny, with six strong conical radial spines, opposite in pairs on the poles of the three dimensive axes. All three pairs are of different sizes, the length of each spine corresponding nearly to the size of the shell-axis, of which it is the prolongation. Network of the shell subregular, with circular pores twice as broad as the bars; ten on the half meridian, eight on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4.

Dimensions.—Length of the shell 0.12, breadth 0.09, thickness 0.06; pores 0.01, bars 0.005.

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

5. Larcarium octostylum, n. sp.

Shell thorny, with eight thin cylindrical radial spines, opposite in pairs in two crossed diagonal planes. Network of the shell irregular, with roundish pores, twice to four times as broad as the bars; nine to eleven on the half meridian, five to seven on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5.

Dimensions.—Length of the shell 0.11, breadth 0.09, thickness 0.07; pores 0.006 to 0.012, bars 0.003.

Habitat.—Pacific, central area, Station 267, surface.

6. Larcarium polystylum, n. sp.

Shell thorny, with numerous (twenty to thirty) stronger conical radial spines, about as long as the shortest axis of the shell. Network of the shell irregular, with roundish pores, twice to four times as broad as the bars; seven to eight on the half meridian, five to six on the half equator. Proportion of the three dimensive axes = 1 : 2 : 3.

Dimensions.—Length of the shell 0.09, breadth 0.06, thickness 0.03; pores 0.006 to 0.012, bars 0.003.

Habitat.—South Atlantic, Station 323, surface.

7. Larcarium chætostylum, n. sp.

Shell bristly, with very numerous (sixty to eighty or more) very thin, bristle-like, radial spines, somewhat longer than the longest axis of the shell. Network irregular, with very small roundish pores, about the same size as the bars; sixteen to eighteen on the half meridian, thirteen to fifteen on the half equator. Proportion of the three dimensive axes = 1 : 1.5 : 2.

Dimensions.—Length of the shell (without spines) 0.13, breadth 0.1, thickness 0.07; pores and bars 0.004 to 0.006.

Habitat.—Pacific, central area, Station 273, surface.

Subfamily 2. Coccolarcida, Haeckel.

Definition.—Larcarida with encased lentelliptical shell, composed of two or more concentric lentelliptical latticed shells, which are united by radial beams (at least one inner medullary shell and one outer cortical shell).

Genus 268. Coccolarcus,^[3] n. gen.

Definition.—Larcarida with two concentric latticed shells, an outer lentelliptical cortical shell, and an inner (spherical or lentelliptical) medullary shell, both connected by radial beams. Surface without radial spines.

The genus Coccolarcus differs from Cenolarcus by the possession of an internal medullary shell. This is quite simple, either spherical or lentelliptical, and connected with the outer cortical shell by a number of radial beams. In the similar Larnacilla this connection is effected by four internal latticed lamellæ (the half lateral wings of the transverse girdle); therefore we find here four internal gates (on the poles of the principal axis), absent in Coccolarcus.

1. Coccolarcus lentellipsis, n. sp.

Cortical shell with smooth surface and regular network; pores circular, twice as broad as the bars; about thirteen on the half meridian, eleven on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5. Medullary shell spherical, half as broad as the transverse radius.

Dimensions.—Principal axis (or length) of the cortical shell 0.15, transverse axis (or breadth) 0.12, sagittal axis (or thickness) 0.09; pores 0.01, bars 0.005; diameter of the medullary shell 0.03.

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

2. Coccolarcus platellipsis, n. sp.

Cortical shell with thorny surface and irregular network; pores roundish, twice to three times as broad as the bars; sixteen to eighteen on the half meridian, ten to twelve on the half equator. Proportion of the three dimensive axes = 1 : 2 : 3. Medullary shell lentelliptical, one-third as large as the cortical shell.

Dimensions.—Length of the cortical shell 0.17, breadth 0.11, thickness 0.06; pores 0.008 to 0.012, bars 0.004; medullary shell 0.03 to 0.06.

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

Genus 269. Larcidium,^[4] n. gen.

Definition.—Larcarida with two concentric latticed shells, an outer lentelliptical cortical shell, and an inner (spherical or lentelliptical) medullary shell, both connected by radial beams. Surface covered with radial spines.

The genus Larcidium differs from the foregoing Coccolarcus only in the possession of radial spines, and bears to it the same relation that Larcarium does to Cenolarcus. The spines are commonly symmetrically disposed, opposite in pairs in the dimensive axes, sometimes also in diagonal axes.

1. Larcidium dissacanthum, n. sp.

Cortical shell with thorny surface and regular network; pores circular, hexagonally framed, three times as broad as the bars; about thirteen on the half meridian, eleven on the half equator. Proportion of the three dimensive axes = 2 : 3 : 5. Medullary shell spherical, one-fourth as broad as the cortical, connected with it by two thin beams, lying in the principal axis, and prolonged on its poles into two strong conical spines, somewhat longer than the greatest axis.

Dimensions.—Length of the cortical shell (or principal axis) 0.15, breadth 0.09, thickness 0.07; pores 0.015, bars 0.005; medullary shell 0.025.

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

2. Larcidium hexacanthum, n. sp.

Cortical shell with smooth surface and regular network; pores circular, twice as broad as the bars; about eleven on the half meridian, nine on the half equator. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell spherical, one-third as broad as the cortical. On the surface six strong, three-sided pyramidal spines, all about as long as the breadth of the cortical shell.

Dimensions.—Length of the cortical shell 0.12, breadth 0.1, thickness 0.08; pores 0.01, bars 0.005; medullary shell 0.035.

Habitat.—Pacific, central area. Station 266, surface.

3. Larcidium axacanthum, n. sp.

Cortical shell with rough surface and irregular network; pores roundish, twice to four times as broad as the bars; about fifteen to nineteen on the half meridian, twelve to fourteen on the half equator. Proportion of the three axes = 2 : 3 : 4. Medullary shell lentelliptical, of the same form and structure as the cortical, but only one-third as large, connected with it by six thin radial beams, lying in pairs in the three dimensive axes; on the outside they are prolonged into six strong conical radial spines, which are in pairs of different size (as in Larcarium axostylum); the length of each spine nearly equals the axis of the cortical shell, of which it is the prolongation.

Dimensions.—Length of the cortical shell (and the principal spines) 0.18, breadth of it (and length of the lateral spines) 0.135, thickness of it (and length of the sagittal spines) 0.09; pores 0.005 to 0.013, bars 0.003.

Habitat.—Pacific, central area, Station 271, surface.

4. Larcidium octacanthum, n. sp.

Cortical shell thorny, with irregular network; pores roundish, once to four times as broad as the bars; about thirteen to fifteen on the half meridian, eleven to thirteen on the half equator. Proportion of the three axes = 1 : 2.5 : 4. Medullary shell lentelliptical, one-fifth as large as the cortical, connected with it by eight radial beams, which are situated in two crossed diagonal planes (opposite in pairs), and are prolonged on the surface into eight long and thin cylindrical radial spines similar to Tetrapyle octacantha.

Dimensions.—Length of the cortical shell 0.16, breadth 0.11, thickness 0.045; pores 0.003 to 0.012, bars 0.003; medullary shell 0.02 to 0.03.

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

5. Larcidium dodecanthum, n. sp. (Pl. 50, figs. 8, 8a).

Cortical shell rough, with irregular network; pores roundish, twice to four times as broad as the bars; about twelve to fourteen on the half meridian, eight to ten on the half equator. Proportion of the three axes = 2 : 3 : 4. Medullary shell lentelliptical, one-third as large as the cortical, connected with it by twelve thin radial beams, which are prolonged outside into twelve strong conical radial spines, about half as long as the breadth of the shell.

Dimensions.—Length of the cortical shell 0.14, breadth 0.1, thickness 0.07; pores 0.008 to 0.015, bars 0.004; medullary shell 0.04 to 0.05.

Habitat.—South Pacific, Station 288, surface.

6. Larcidium polyacanthum, n. sp.

Cortical shell spiny, with irregular network; pores roundish, once to twice as broad as the bars; about ten to twelve on the half meridian, six to eight on the half equator. Proportion of the three axes = 1 : 2 : 3. Medullary shell lentelliptical, half as large as the cortical shell, connected with it by numerous (twenty to twenty-five) radial beams, which are prolonged outside into three-sided pyramidal spines, about as long as the breadth of the shell.

Dimensions.—Length of the cortical shell 0.18, breadth 0.12, thickness 0.06; pores 0.01 to 0.015, bars 0.008; medullary shell 0.03 to 0.09.

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

Subfamily 3. Spongolarcida, Haeckel.

Definition.—Larcarida with spongy lentelliptical shell (with or without enclosed medullary shell).

Genus 270. Spongolarcus,^[5] n. gen.

Definition.—Larcarida with lentelliptical spongy shell, containing a central cavity of the same form, without medullary shell (without radial spines).

The genus Spongolarcus differs from Cenolarcus (its probable ancestral form) only in the development of spongy framework forming the wall of the hollow lentelliptical shell. It corresponds, therefore, to Plegmosphæra among the Sphæroidea, and to Spongellipsis among the Prunoidea. From these two similar spongy Sphærellaria it differs in its characteristic lentelliptical form, with three dimensive axes of unequal length.

1. Spongolarcus lentellipsis, n. sp.

Spongy network of the shell very loose, its meshes fifteen to twenty times as broad as the bars. Surface of the shell nearly smooth; diameter of its internal cavity twice as large as the thickness of its wall. Proportion of the three dimensive axes = 2 : 3 : 4.

Dimensions.—Length 0.16, breadth 0.12, height 0.08; thickness of the spongy wall 0.05.

Habitat.—Pacific, central area, Station 274, surface.

2. Spongolarcus triaxonius, n. sp.

Spongy network of the shell rather loose, its meshes twelve to sixteen times as broad as the bars. Surface of the shell rough; diameter of its internal cavity about eight times as large as the thickness of its wall. Proportion of the three dimensive axes = 2 : 2.5 : 3.

Dimensions.—Length 0.25, breadth 0.2, height 0.16; thickness of the spongy wall 0.025.

Habitat.—North Pacific, Station 253, surface.

3. Spongolarcus dimensivus, n. sp.

Spongy network of the shell dense, its meshes four to eight times as broad as the bars. Surface of the shell thorny; diameter of its internal cavity about fifteen times as large as the thickness of its wall. Proportion of the three dimensive axes = 3 : 4 : 5.

Dimensions.—Length 0.2, breadth 0.16, height 0.12; thickness of the spongy wall 0.01.

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

4. Spongolarcus amphicentria, Haeckel.

? Amphicentria salpa, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 296; Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, Taf. ii. fig. 18. ? Spongurus salpa, Haeckel, 1862, Monogr. d. Radiol., p. 466.

Spongy network of the shell compact, its meshes about the same breadth as the bars. Surface of the shell spiny, with some larger spines around the poles of the axis; diameter of the internal cavity about six times as large as the thickness of its wall. Proportion of the three dimensive axes = 1 : 2 : 3. (Perhaps this Spongolarcus is identical with Amphicentria salpa, very imperfectly described and figured by Ehrenberg, loc. cit.?)

Dimensions.—Length 0.14, breadth 0.09, height 0.05; thickness of the spongy wall 0.015.

Habitat.—North Atlantic; off Greenland, 1000 fathoms, Ehrenberg; Station 64, depth (2700) fathoms.

Genus 271. Stypolarcus,^[6] n. gen.

Definition.—Larcarida with lentelliptical spongy shell, composed of compact spongy framework, without central cavity and medullary shell (without radial spines).

The genus Stypolarcus differs from Spongolarcus in the absence of any central cavity. This is quite filled up by spongy framework, which forms the whole mass of the lentelliptical body. Stypolarcus bears therefore the same relation to Spongolarcus that Styptosphæra does to Plegmosphæra.

1. Stypolarcus spongiosus, n. sp.

Lentelliptical shell composed in the whole mass of loose, spongy framework of similar texture, with irregular meshes, about ten to twenty times as broad as the thin bars. Surface rough, without radial spines. Proportion of the three axes = 3 : 4 : 5.

Dimensions.—Length 0.2, breadth 0.16, height 0.12.

Habitat.—Antarctic Ocean, Station 157, depth 1950 fathoms.

Family XXV. Larnacida, Haeckel, 1883 (Pl. 50, figs. 3-8).

Definition.—Larcoidea with a regular, completely latticed, lentelliptical cortical shell, without open gates and annular constrictions; either this cortical shell or the enclosed medullary shell is trizonal, composed of three elliptical, latticed, dimensive girdles of different sizes, perpendicular one to another.

The family Larnacida immediately follows the Larcarida as the next simple group of all Larcoidea; some genera of both groups (such as Larnacalpis and Coccolarcus, or Larnacantha and Larcidium) may easily be confounded from their being so much alike. In both the lentelliptical shell is composed of two concentric shells, an inner (medullary) and an outer (cortical) shell. But the connection between these shells and the construction of the inner shell is quite different in the two groups. Whilst in the Larcarida the medullary shell is connected with the cortical shell simply by radial beams, here in the Larnacida this connection is effected by two latticed lamellæ, which are the lateral wings of a transverse girdle. Therefore we encounter here for the first time that peculiar mode of growth which characterises the greater part of the Larcoidea, but particularly the Pylonida. But whilst in the Pylonida between the three crossed lattice-girdles, remain four open gates, here in the Larnacida the gates become closed by lattice-work; the lentelliptical cortical shell becomes perfect.

The most simple genus of Larnacida, and no doubt the common ancestral form of this whole family, is Larnacilla (Pl. 50, figs. 1, 1a, 1b). The most important shell of this typical genus is composed of a simple lentelliptical medullary shell and of three elliptical latticed girdles surrounding it, perpendicular one to another. These three "dimensive girdles" lie in the perimeter of the three dimensive planes, the minor (and first) in the equatorial plane, the second (and major) in the lateral plane, the third (and intermediate) in the sagittal plane. Therefore we have before us the same "trizonal shell" as in the important genus Trizonium among the Pylonida. But whilst in Trizonium, as in all Pylonida, the four gates between the girdles remain open, here in Larnacilla they become perfectly closed by lattice-work.

The formation of the typical "Larnacilla-shell" begins with a simple, spherical or lentelliptical lattice-shell, from both sides of which arise two latticed "lateral wings" opposite on the poles of the transverse axis. These two wings are comparable to the lateral chambers of Tholartus (among the Tholonida), but differ by two large openings. Each wing is a short cylindrical tube with latticed wall, open at both ends; the axis of the tube (going through the centre of the open ends) is parallel to the principal axis of the whole shell (and of the central chamber). Therefore both wings form together a transverse ring, the middle of which encloses the central chamber. The distal parts of both wings grow towards the poles of the principal axis; if they became united here, the second (lateral) girdle would be complete. Between it and the first girdle four open gates remain ("Tetrapyle"); but these become overgrown by the third or sagittal girdle, and at last the gates between this and the two other girdles become closed by lattice-work. This perfect fenestration of the trizonal cortical shell, and the complete closing of the gates between the girdles by network, is the only difference between Trizonium and Larnacilla.

In Larnacilla and in the nearly allied Larnacidium (only differing by radial spines on the surface) the "trizonal shell" is an external or "cortical shell," enclosing the central capsule, the interior of which only contains the simple central chamber and the jointed proximal parts of both lateral wings. In the other genera of Larnacida (by proceeding growth) this trizonal Larnacilla-shell becomes enclosed by the growing central capsule and is now only a "medullary shell," whilst on the outside of the central capsule in the same manner is developed an outer cortical shell (Larnacalpis, Larnacantha); and perhaps the same process may be repeated. But sometimes also this cortical shell becomes doubled by a simple envelop of network (Larnacoma). In the Larnacospongida the cortical shell is composed of a spongy framework (corresponding to the Spongolarcida in the foregoing family).

The lattice-work of the Larnacida is commonly irregular (as in most other Larcoidea), and its pores have little signification for the different species. On the outer surface often arise radial spines, symmetrically disposed either in dimensive planes or in diagonal planes.

The central capsule is constantly a true lentellipsis or a "triaxial ellipsoid," characterised by three halving, elliptical dimensive planes, perpendicular one to another. It bears a different relation to the skeleton in the two subfamilies of Larnacida. In the first subfamily, the Larnacillida (Larnacilla, Larnacidium), the central capsule encloses only the simple spherical or lentelliptical central chamber ("simple medullary shell"), and is enveloped by the trizonal cortical shell. In the other subfamily, the Larnacalpida (Larnacalpis, Larnacospongus, &c.), this trizonal "Larnacilla-shell" becomes enclosed by the overgrowing central capsule, which now becomes enveloped by an external, latticed or spongy, lentelliptical "cortical shell."

Synopsis of the Genera of Larnacida.

II. Subfamily Larnacillida. Medullary shell simple, spherical or subspherical. Cortical shell lentelliptical, trizonal; between them four gates.			$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Shell without radial spines,			272. Larnacilla.
				Shell with radial spines,			273. Larnacidium.
II. Subfamily Larnacalpida. Medullary shell Larnacilla-shaped, double; the inner spherical or subspherical, the outer lentelliptical and trizonal.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Cortical shell simple or double, but not spongy.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Cortical shell simple.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Without radial spines,	274. Larnacalpis.
						With radial spines,	275. Larnacantha.
				Cortical shell double, without radial spines,			276. Larnacoma.
		Cortical shell simple or double, wholly or partly spongy.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Shell without radial spines,			277. Larnacospongus.
				Shell with radial spines,			278. Larnacostupa.

Subfamily 1. Larnacillida, Haeckel.

Definition.—Larnacida with a simple, spherical or lentelliptical, medullary shell, connected by the lateral wings of a latticed transverse girdle with the simple lentelliptical trizonal cortical shell; the central capsule encloses the former and is enveloped by the latter.

Genus 272. Larnacilla,^[7] n. gen.

Definition.—Larnacida with a simple lentelliptical cortical shell, connected by the lateral wings of a latticed transverse girdle with the simple, spherical or lentelliptical, medullary shell. Surface without radial spines.

The genus Larnacilla represents the most simple form of Larnacida, and at the same time the most important common ancestral form, from which the greater number of Larcoidea may be derived, viz., all those genera which possess the characteristic "Larnacilla-shaped medullary shell." This typical form of medullary shell may be derived from the genus Trizonium among the Pylonida by the closing of the four open gates of this genus. The free opening of these four gates becomes overgrown and closed by lattice-work, developed from the free edges of the three crossed girdles, and thus finally all three girdles are united in the form of a simple lentelliptical shell (Pl. 50, figs. 1, 1a, 1b). Seen from the sagittal poles (or from the poles of the shortest axis, fig. 1), the shell exhibits on both sides of the small spherical medullary shell the two lateral wings of the transverse girdle from the face; seen from the lateral poles (or from the poles of the transverse axis, fig. 1a), one of these wings appears in the optical section as an oblong ring, which seemingly encloses the concentric medullary shell, and on both sides is grown together with the sagittal girdle; seen from the principal poles (or from the poles of the longitudinal axis, fig. 1b), both wings exhibit their elliptical opening (at the right and left from the central medullary shell). The two concentric shells are only connected by the two lateral tube-like wings of the transverse girdle; the lateral and the sagittal girdles have no connection with the medullary shell. The latter is sometimes spherical, at other times lentelliptical.

1. Larnacilla typus, n. sp. (Pl. 50, fig 1, 1a, 1b).

Cortical shell with smooth surface and with subregular network; pores twice as broad as the bars; about twelve pores on the half meridian, ten on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4. Internal four gates (between transverse and lateral girdles) roundish-triangular, little broader than high. Medullary shell spherical, scarcely one-third as broad as the lentelliptical cortical shell.

Dimensions.—Length of the cortical shell (or principal axis) 0.13, breadth of it (or transverse axis) 0.1, height of it (or sagittal axis) 0.07; pores 0.006, bars 0.003; medullary shell (diameter) 0.03.

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

2. Larnacilla prometor, n. sp.

Cortical shell with rough surface and regular network; pores three times as broad as the bars; about ten on the half meridian, eight on the half equator. Proportion of the three axes = 1 : 2 : 3. Internal four gates (between transverse and lateral girdles) kidney-shaped, twice as broad as high. Medullary shell lentelliptical, of the same form as the external cortical shell, but only one third as large.

Dimensions.—Length of the cortical shell 0.15, breadth 0.1, height 0.05, pores 0.015, bars 0.005; medullary shell 0.02 to 0.05.

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

3. Larnacilla subglobosa, n. sp.

Cortical shell nearly spherical, with thorny surface and irregular network; pores roundish, twice to four times as broad as the bars; twelve to sixteen in the half circumference. Proportion of the three axes very little different = 1.3 : 1.4 : 1.5. Internal four gates elliptical, one and a half times as broad as high. Medullary shell spherical, one-fourth as broad as the cortical shell.

Dimensions.—Length of the cortical shell 0.15, breadth 0.14, height 0.13; pores 0.006 to 0.012, bars 0.003; medullary shell 0.035.

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

4. Larnacilla medullaris, n. sp.

Cortical shell lentelliptical, with smooth surface and irregular network; pores roundish, very small, scarcely as broad as the bars; about eight to nine on the half meridian, six to seven on the half equator. Proportion of the three axes = 3 : 4 : 6. Internal four gates elliptical. Medullary shell spherical, scarcely one-third as broad as the cortical shell. (This small species may be only the medullary shell of some other Larcoid, the cortical shell of which is not yet formed.)

Dimensions.—Length of the cortical shell 0.06, breadth 0.04, height 0.03; pores and bars about 0.004; medullary shell 0.013.

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

Genus 273, Larnacidium,^[8] n. gen.

Definition.—Larnacida with a simple lentelliptical cortical shell, connected by the lateral wings of a latticed transverse girdle with the simple, spherical or lentelliptical, medullary shell. Surface armed with radial spines.

The genus Larnacidium has the same shell-formation as the foregoing Larnacilla, and differs from it only in the possession of radial spines on the surface, which in all known species exhibit a symmetrical disposition. From the nearly allied genus Larcidium it differs in the characteristic mode of connection between the two shells, owing to the different kind of growth. In Larcidium this connection is effected only by radial beams, whereas in Larnacidium (as in all Larnacida) by two lateral latticed tubes, the wings of the primary transverse girdle.

1. Larnacidium staurobelonium, n. sp.

Cortical shell smooth, with four strong conical, radial spines in the lateral plane, opposite in pairs, two on the poles of the principal and two on the poles of the transverse axis. Pores subregular, circular, twice as broad as the bars; about twelve on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell spherical, one-third as broad as the cortical shell.

Dimensions.—Length of the cortical shell 0.12, breadth 0.09, height 0.06; pores 0.008, bars 0.04; medullary shell 0.03.

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

2. Larnacidium hexabelonium, n. sp.

Cortical shell thorny, with six strong, three-sided pyramidal, radial spines, lying opposite in pairs on the poles of the three dimensive axes. Pores subregular, circular, three times as broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell spherical, one-third as broad as the cortical shell.

Dimensions.—Length of the cortical shell 0.14, breadth 0.11, height 0.08; pores 0.01, bars 0.003; medullary shell 0.04.

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

3. Larnacidium polybelonium, n. sp.

Cortical shell very spiny, with numerous (twenty to thirty or more) larger thin radial spines, about as long as the shell. Pores irregular, twice to five times as broad as the bars; about sixteen on the half meridian. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell lentelliptical, half as large as the cortical shell.

Dimensions.—Length of the cortical shell 0.11, breadth 0.09, height 0.07; pores 0.004 to 0.01, bars 0.002; length of the medullary shell 0.06, breadth 0.05, height 0.04.

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

Subfamily 2. Larnacalpida, Haeckel.

Definition.—Larnacida with a double, trizonal, Larnacilla-shaped medullary shell, enclosed in the central capsule, and enveloped by a simple or double, latticed or spongy, lentelliptical, cortical shell.

Genus 274. Larnacalpis,^[9] n. gen.

Definition.—Larnacida with a simple lentelliptical cortical shell, without radial spines. Medullary shell double, Larnacilla-shaped.

The genus Larnacalpis represents the most simple form of the sub-family Larnacalpida, and is very important as the common original form of all those Larcoidea in which a double Larnacilla-shaped medullary shell is surrounded by a simple, perfectly closed, latticed, lentelliptical cortical shell. Therefore the same typical, trizonal, lentelliptical shell, which in Larnacilla represents the external envelop (or cortical shell) of the central capsule, here in Larnacalpis becomes enclosed as an internal nucleus (or medullary shell) in the interior of the central capsule, and this latter becomes overgrown by a new lentelliptical cortical shell. The connection between the two shells of Larnacalpis is either effected by a number of radial beams (e.g., in Larnacalpis triaxonia by six beams situated in the three dimensive axes), or by two lateral, latticed, tube-like wings, which are repetitions of the smaller lateral wings connecting its external shell with the internal medullary shell (as in Larnacalpis lentellipsis). The latter species may be regarded as a Pylonium with a completely latticed shell.

1. Larnacalpis lentellipsis, n. sp. (Pl. 50, figs. 2, 2a, 2b).

Cortical shell with thorny surface and irregular network; pores roundish, twice to four times as broad as the bars; about sixteen on the half meridian, twelve on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4. Medullary shell one-third as large as the cortical, with four elliptical internal gates, connected with it by two opposite beams in the principal axis and by two latticed wings in the transverse axis; therefore between the two shells are four large kidney-shaped gates, halved by the polar beams (as in Octopyle).

Dimensions.—Length of the cortical shell (or principal axis) 0.14, breadth (or transverse axis) 0.11, height (or sagittal axis) 0.07; pores 0.01 to 0.02, bars 0.005; length of the medullary shell 0.05, breadth 0.04, height 0.03.

Habitat.—Pacific, central area, Station 273, depth 2600 fathoms.

2. Larnacalpis phacodiscus, n. sp.

Cortical shell with thorny surface and regular network; pores circular, twice as broad as the bars; about ten on the half meridian, eight on the half equator. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell half as large as the cortical, with four kidney-shaped internal gates.

Dimensions.—Length of the cortical shell 0.13, breadth 0.11, height 0.09; pores 0.012, bars 0.006; length of the medullary shell 0.06, breadth 0.045, height 0.03.

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

3. Larnacalpis macrococcus, n. sp.

Cortical shell with spiny surface and regular network; pores circular, small, of the same breadth as the bars; about twenty-two on the half meridian, nineteen on the half equator. Proportion of the three axes = 2 : 3 : 4. Medullary shell two-thirds as large as the cortical, with four wide internal semicircular gates.

Dimensions.—Length of the cortical shell 0.1, breadth 0.075, height 0.05; pores and bars 0.003; length of the medullary shell 0.066, breadth 0.05, height 0.032.

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

4. Larnacalpis subsphærica, n. sp.

Cortical shell with rough surface and irregular network; roundish pores twice to five times as broad as the bars; about twenty-four on the half meridian, twenty-one on the half equator. Proportion of the three axes = 1.2 : 1.3 : 1.4. Medullary shell half as large as the cortical, with four elliptical internal gates.

Dimensions.—Length of the cortical shell 0.14, breadth 0.13, height 0.12; pores 0.004 to 0.01, bars 0.002; length of the medullary shell 0.08, breadth 0.07, height 0.06.

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

5. Larnacalpis triaxonia, n. sp. (Pl. 50, fig. 3).

Cortical shell with smooth surface and peculiar network, composed of four meridian rows of larger pores (five large elliptical pores on each half meridian, the largest in the equator) and numerous small irregular pores between them. Proportion of the three axes = 2 : 3 : 4. Medullary shell with four semicircular internal gates, about one-fourth as large as the cortical, connected with it by six thin radial beams, opposite in pairs in the three dimensive axes.

Dimensions.—Length of the cortical shell 0.14, breadth 0.1, height 0.07; large pores 0.03, small pores 0.002 to 0.01, bars 0.002 to 0.01; length of the medullary shell 0.04, breadth 0.03, height 0.02.

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

Genus 275. Larnacantha,^[10] n. gen.

Definition.—Larnacida with a simple lentelliptical cortical shell, armed with symmetrically disposed radial spines. Medullary shell double, Larnacilla-shaped.

The genus Larnacantha has the same characteristic shell-formation as the foregoing Larnacalpis, and differs from it only in the possession of radial spines, which are symmetrically distributed on the surface in a definite order. Commonly these spines are external prolongations of the internal radial beams, which connect the double Larnacilla-shaped medullary shell with the simple lentelliptical cortical shell.

1. Larnacantha dissacantha, n. sp.

Cortical shell smooth, with two large cylindrical spines, opposite on the poles of the principal axis, and somewhat longer than it. Pores regular, circular, three times as broad as the bars; about eleven on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell one-third as large as the cortical shell.

Dimensions.—Length of the cortical shell (principal axis) 0.13, breadth (transverse axis) 0.1, height (sagittal axis) 0.07; pores 0.009, bars 0.003; length of the Larnacilla-shaped medullary shell 0.045.

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

2. Larnacantha stauracantha, n. sp.

Cortical shell smooth, with four large conical spines in the lateral plane, two larger opposite on the poles of the principal, two smaller on those of the transverse axis. Pores regular, circular, twice as broad as the bars; about seventeen on the half meridian. Proportion of the three axes = 3 : 3.5 : 4. Medullary shell one-third as large as the cortical shell.

Dimensions.—Length of the cortical shell 0.15, breadth 0.13, height 0.11; pores 0.008, bars 0.004; length of the medullary shell 0.05.

Habitat.—Pacific, central area, Station 274, surface.

3. Larnacantha quadricornis, n. sp.

Cortical shell spiny, with four strong, horn-like curved spines in the lateral plane, opposite in pairs on the poles of the crossed diagonal axes. Pores irregular, roundish, twice to four times as broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell one-third as large as the cortical shell.

Dimensions.—Length of the cortical shell 0.14, breadth 0.11, height 0.07; pores 0.006 to 0.012, bars 0.003; length of the medullary shell 0.05.

Habitat.—Pacific, central area, Station 270, surface.

4. Larnacantha hexacantha, n. sp. (Pl. 50, fig. 4).

Cortical shell thorny, with six strong conical radial spines in the lateral plane, two opposite on the poles of the principal axis, four others opposite in pairs on the poles of the two crossed diagonal axes. Pores with peculiar distribution; twelve large elliptical pores (nearly of the size of the medullary shell) symmetrically disposed in four crossed meridians (between the sagittal and the lateral meridians), separated by bands of smaller irregular pores. Proportion of the three axes = 3 : 4 : 5. Medullary shell hexagonal, one-third as large as the cortical shell.

Dimensions.—Length of the cortical shell 0.14, breadth 0.11, height 0.08; large pores 0.04, small pores 0.003 to 0.01, bars 0.004; length of the medullary shell 0.05.

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

5. Larnacantha bicruciata, n. sp. (Pl. 50, fig. 5).

Cortical shell thorny, in the lateral plane with eight strong conical radial spines, alternating with eight smaller spines; four of the eight stronger spines opposite on the poles of the principal and transverse axes (in the figure 5, by mistake, not represented large enough), four others between those, opposite on the poles of the two crossed diagonal axes. Pores with a peculiar disposition; on both flat sides of the lentellipsis an elliptical ring of eight large elliptical pores (alternating with the eight stronger radial spines), separated by bands of smaller irregular pores. Proportion of the three axes = 2 : 3 : 4. Medullary shell nearly half as long as the cortical shell.

Dimensions.—Length of the cortical shell 0.16, breadth 0.13, height 0.08; large pores 0.03, small pores 0.003 to 0.01, bars 0.006; length of the medullary shell 0.07.

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

6. Larnacantha octacantha, n. sp.

Cortical shell thorny, with eight long and thin, cylindrical, radial spines, lying opposite in pairs in two crossed diagonal planes. Pores irregular, roundish, twice to five times as broad as the bars; about sixteen on the half meridian. Proportion of the three axes = 1 : 1⅓ : 2. Medullary shell scarcely one-fourth as long as the cortical shell. (This species resembles closely the common Tetrapyle octacantha, from which it seems to be developed by a complete over-growing of the four gates, which become closed by a network connecting the free edges of the transverse and lateral girdles.)

Dimensions.—Length of the cortical shell 0.18, breadth 0.13, height 0.1; pores 0.005 to 0.015, bars 0.003; length of the medullary shell 0.04.

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

7. Larnacantha cladacantha, n. sp.

Cortical shell very spiny, with eight longer ramified spines, lying opposite in pairs in two crossed diagonal planes; each spine with two to six irregular, lateral branches. Pores irregular, roundish, twice to three times as broad as the bars; about twelve on the half meridian. Proportion of the three axes = 5 : 6 : 7. Medullary shell nearly half as long as the cortical shell. (Differs from the foregoing by the branching spines end the larger medullary shell.)

Dimensions.—Length of the cortical shell 0.15, breadth 0.13, height 0.11; pores 0.01 to 0.015, bars 0.005; length of the medullary shell 0.07.

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

8. Larnacantha prismatica, n. sp. (Pl. 50, fig. 6).

Cortical shell smooth, four-sided prismatic, with eight short, parallel, three-sided pyramidal spines; these lie opposite in pairs in four parallel longitudinal lines, as prolongations of the four lateral edges of the prism, and arise from its eight corners. Pores regular, circular, three times as broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell half as long as the cortical shell.

Dimensions.—Length of the cortical shell 0.11, breadth 0.07, height 0.05; pores 0.006, bars 0.002; length of the medullary shell 0.06.

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

9. Larnacantha decacantha, n. sp.

Cortical shell thorny, with ten short and stout, conical, radial spines, two opposite on the poles of the principal axis (as prolongations of inner axial beams), eight others opposite in pairs in two crossed diagonal planes. Pores irregular, roundish, twice to four times as broad as the bars; about sixteen on the half meridian. Proportion of the three axes = 3 : 3.75 : 4. Medullary shell about one-third as long as the cortical shell.

Dimensions.—Length of the cortical shell 0.16, breadth 0.15, height 0.12; pores 0.008 to 0.016, bars 0.004; length of the medullary shell 0.06.

Habitat.—North Atlantic, Station 354, surface.

10. Larnacantha dodecantha, n. sp.

Cortical shell nearly smooth, but with twelve strong conical radial spines; four in the lateral plane opposite in pairs (two on the poles of the principal, and two on the poles of the transverse axis); eight others opposite in pairs in two crossed diagonal planes. Pores with a peculiar disposition: twelve large elliptical pores in two crossed meridian planes (alternating with the twelve spines), separated by bands of irregular small pores. Proportion of the three axes = 1 : 1.5 : 2. Medullary shell hexagonal, one-third as long as the cortical shell.

Dimensions.—Length of the cortical shell 0.15, breadth 0.11, height 0.08; large pores 0.03, small pores 0.005 to 0.01, bars 0.003; length of the medullary shell 0.05.

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

11. Larnacantha drymacantha, n. sp.

Cortical shell very spiny, on the whole surface covered with a forest of numerous (thirty to fifty or more) large branched spines, about the length of the shell; each spine with three to nine lateral branches, simple or forked (very similar to Cromyodrymus abietinus, Pl. 30, fig. 6). Pores very irregular, roundish. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell half as long as the cortical shell.

Dimensions.—Length of the cortical shell 0.16, breadth 0.13, height 0.1; pores 0.005 to 0.015, bars 0.03; length of the medullary shell 0.08.

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

Genus 276. Larnacoma,^[11] n. gen.

Definition.—Larnacida with double lentelliptical cortical shell, without radial spines. Medullary shell double, Larnacilla-shaped.

The genus Larnacoma has originated from the nearly allied Larnacalpis by duplication of the cortical shell. Whilst in both genera the connection between the Larnacilla-shaped medullary shell and the primary cortical shell is the same, many short radial beams arise from the surface of the latter in Larnacoma, which at constant equal distances from it unite by a network forming the secondary or outer cortical shell. It differs from the similar Druppulida (Cromyodruppa) by the sagittal flattening of the lentelliptical shell and the Larnacilla-form of the double medullary shell.

1. Larnacoma lentellipticum, n. sp.

Shell with smooth surface and elliptical perimeter, one and a third times as long as broad. All four shells lentelliptical. Distance between the two cortical shells about twice as great as the distance of the inner cortical and outer medullary shell. Network of both outer shells irregular, with large roundish pores, twice to six times as broad as the bars.

Dimensions.—Length (or principal axis) of the first (innermost) shell 0.03, second 0.08, third 0.16, fourth (outermost) 0.27, breadth (or transverse axis) corresponding—(A) 0.02, (B) 0.05, (C) 0.11, (D) 0.2.

Habitat.—South Atlantic, Station 323, depth 1900 fathoms.

2. Larnacoma quadruplex, n. sp.

Shell with thorny surface and elliptical perimeter, one and a fifth times as long as broad. All four shells lentelliptical. Distance between the two cortical shells somewhat smaller than the distance between the inner cortical and outer medullary shell. Network of both outer shells irregular, with large roundish pores, twice to ten times as broad as the bars.

Dimensions.—Length of the first shell 0.02, second 0.06, third 0.15, fourth 0.24; breadth corresponding—(A) 0.016, (B) 0.04, (C) 0.11, (D) 0.2.

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

3. Larnacoma hexagonium, n. sp.

Shell with thorny surface and hexagonal perimeter, as long as broad. All four shells hexagonal, connected by six piercing radial beams (two in the principal axis, four others in two crossed diagonals). Distance between the two cortical shells somewhat greater than the distance between the inner cortical and outer medullary shell. Network of both outer shells subregular, with small circular pores, twice as broad as the bars.

Dimensions.—Length of the first shell 0.02, second 0.05, third 0.09, fourth 0.16; breadth corresponding—(A) 0.015, (B) 0.035, (C) 0.065, (D) 0.12.

Habitat.—South Atlantic, west of Tristan da Cunha, Station 332, depth 2200 fathoms.

Genus 277. Larnacospongus,^[12] n. gen.

Definition.—Larnacida with spongy lentelliptical cortical shell, without radial spines. Medullary shell double, Larnacilla-shaped.

The genus Larnacospongus differs from the nearly allied genera Larnacalpis and Larnacoma by the spongy texture of the lentelliptical cortical shell whilst the enclosed medullary shell in both genera is the same trizonal Larnacilla-shell. Therefore Larnacospongus (and the following nearly related Larnacostupa) can be derived directly by development of a spongy envelop either from Larnacilla and Larnacalpis, or from Trizonium and Amphipyle. But some species of these spongy genera appear to be derived rather from Tetrapyle or Pylonium, perhaps also from Cubotholus. Their phylogenetic origin may be explained in different ways.

1. Larnacospongus larnacillifer, n. sp.

Cortical shell lentelliptical, one and a half times as long as broad, with rough surface and rather loose spongy framework, directly enclosing a trizonal Larnacilla-shell of the same form, but of only one-third its size.

Dimensions.—Length of the whole shell 0.17, breadth 0.12; length of the medullary shell 0.06, breadth 0.04.

Habitat.—South Atlantic, east coast of Patagonia, Station 319, surface.

2. Larnacospongus tetrapylifer, n. sp.

Cortical shell lentelliptical, one and a third times as long as broad, with thorny surface; composed of an outer envelop of loose spongy framework and an inner lattice-shell with four kidney-shaped gates, like Tetrapyle; the latter encloses a trizonal medullary shell of one-fourth its size.

Dimensions.—Length of the whole shell 0.22, breadth 0.16; length of the medullary shell 0.045, breadth 0.035.

Habitat.—South Atlantic, west of Tristan da Cunha, Station 332, surface.

Genus 278. Larnacostupa,^[13] n. gen.

Definition.—Larnacida with spongy lentelliptical cortical shell, with radial spines on the surface. Medullary shell double, Larnacilla-shaped.

The genus Larnacostupa differs from the preceding Larnacospongus only in the possession of radial spines, covering either the whole surface irregularly or disposed in a certain symmetrical order.

1. Larnacostupa octacantha, n. sp.

Cortical shell lentelliptical, with thorny surface, and rather dense, irregular, spongy framework, which arises from an inner latticed cortical shell, like that of Tetrapyle or Pylonium. This latter is twice as large as the enclosed Larnacilla-shell. Eight long and thin, cylindrical, radial spines, opposite in pairs in two diagonal planes. (Seems to be the common Tetrapyle octacantha, enveloped by an outer spongy framework mantle.)

Dimensions.—Length of the whole shell (without spines) 0.22, breadth 0.16; length of the medullary shell 0.06, breadth 0.04.

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

2. Larnacostupa spinosa, n. sp.

Cortical shell lentelliptical, about one and a half times as long as broad, with very lax and irregular spongy framework, arising from a nearly quadrangular lattice-shell like that of Tetrapyle; this latter encloses a Larnacilla-shell of half its size. Whole surface covered with thin bristle-like radial spines, of about the length of the shell.

Dimensions.—Length of the whole shell (without spines) 0.18, breadth 0.12; length of the medullary shell 0.05, breadth 0.035.

Habitat.—Antarctic Ocean, off Kerguelen, Station 150, surface.

3. Larnacostupa dendrophora, n. sp.

Cortical shell nearly spherical, scarcely longer than broad, with lax, irregular spongy framework, arising from a lentelliptical trizonal medullary shell (like Larnacilla). Whole surface covered with thin arborescent radial spines, about half as long as the shell, each spine with three to six irregular branches.

Dimensions.—Length of the whole shell (without spines) 0.15, breadth 0.13; length of the medullary shell 0.07, breadth 0.04.

Habitat.—Antarctic Ocean, Station 154, surface.

Family XXVI. Pylonida, Haeckel, 1881 (Pl. 9).

Pylonida, Haeckel, 1881, Prodromus, p. 463.

Definition.—Larcoidea with regular, incompletely latticed cortical shell, distinguished by two to four or more symmetrically disposed gates or large fissures remaining between one to three latticed dimensive girdles (perpendicular one to another). One, two, or three concentric systems of such girdles (each system with three girdles) may be developed.

The family Pylonida is the most important and interesting among all the Larcoidea, not only because it is much richer in different and peculiar forms than the other families of this section, but also because it has direct and very complex relations to all the other families of Larcoidea. It is even possible that the Pylonida represent the original ancestral group of the whole section, and that the apparently simpler group of the Larcarida must be derived from the former by retrogressive metamorphosis.

Till the year 1881 the family Pylonida, which here now exhibits ten genera with eighty-six species, was only represented by one single species, accurately described and extensively illustrated by Johannes Müller in 1858, the well known and widely distributed cosmopolitan Tetrapyle octacantha (Abhandl. d. k. Akad. d. Wiss. Berlin, p. 33, Taf. iii.). A slight modification of it was afterwards described by Ehrenberg as Schizomma quadrilobum (Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, Taf. ii. fig. 12). A more accurate description of it, with a good explanation of its characteristic growth, was given in 1879 by Richard Hertwig in his Organismus der Radiolarien (pp. 52-54, Taf. iv. figs. 7, 8; Taf. vi. figs. 2, 5). In my Prodromus (1881, p. 463) I constituted for a large number of allied species, detected in the Challenger collection, the special family Pylonida, and distinguished among it twelve different genera. However, I think it now better to restrict the definition of the family as given in the above definition, and to remove from it a number of genera formerly with it united, as the genera Triopyle and Hexapyle, appertaining to the Discoidea.

The characteristic type of all true Pylonida is clearly demonstrated by their peculiar mode of growth, the consequence of which is the imperfect lattice-work of the fenestrated larcoid shell. This remarkable growth is effected by the development of elliptical latticed girdles (or rings), which enclose a quite simple, spherical, subspherical, or lentelliptical primordial shell. The girdles lie in three different planes, perpendicular to one another, and are of different sizes; each girdle being somewhat larger than the foregoing and somewhat smaller than the following girdle. Between these latticed girdles remain on the surface of the shell large openings or "gates," which are not closed by network, and it is just the symmetrical disposition and form of these open "gates," separated and enclosed by the fenestrated girdles, which give to the Pylonida their characteristic appearance.

To understand clearly this peculiar constitution of the Pylonida-shell by a system of alternating girdles, developing one after the other it is indispensable to pay careful attention to the three different elliptical dimensive planes, which characterise all Larcoidea, and to the three different dimensive axes, which bisect those planes. The girdle which first develops around simple primordial shell or central chamber is the transverse girdle, lying in the equatorial plane; then comes, secondly, the lateral girdle, lying in the lateral plane; and thirdly follows the sagittal girdle, lying in the sagittal or median plane. The three simplest genera of the Pylonida—Monozonium, Dizonium, Trizonium—represent these three different stages, with one, two, or three girdles. These three genera constitute the first subfamily, Haplozonaria (with one single system of girdles); all three girdles lie in the surface of a simple lentelliptical cortical shell.

From this first subfamily the other two subfamilies of Pylonida must be derived, by repetition of the same characteristic process of growth. In the Diplozonaria a second system of girdles has been developed, constituting a second (outer) cortical shell of lentelliptical form, concentric with the first. Also in this second system the transverse girdle is first developed, secondly the lateral girdle, thirdly the sagittal girdle. The three genera Amphipyle, Tetrapyle (with Octopyle), and Pylonium represent these three different stages of growth.

Commonly the growth of the Pylonida stops with the completion of the second system but sometimes the same process is once repeated and a third system of girdles is formed, constituting a third lentelliptical shell; in this case also the succession of the three latticed girdles is the same; firstly the (third) transverse girdle is formed, secondly the (third) lateral girdle, and thirdly the (third) sagittal girdle. Each of these three girdles of the third system encloses concentrically the corresponding girdles of the second and first system. The three corresponding genera of this third subfamily (Triplozonaria) are Amphipylonium, Tetrapylonium, and Pylozonium. But in general this highest number of girdles (nine) is very seldom reached; commonly the growth of the Pylonida stops with five girdles (Tetrapyle and Octopyle). More than nine girdles I have never observed, though there remains the possibility of the apposition of a fourth system owing to the peculiar imperfect character of the growth itself.

The central or primordial chamber of the shell, with which in all Pylonida the shell-building commences, is a quite simple, very small fenestrated shell. Commonly one sees on the surface only five to ten small pores (three to four on the diameter). Its form seems to be sometimes spherical, sometimes elongated, ellipsoidal or probably lentelliptical. It may be originally a small Cenolarcus. This simple central chamber, the true "medullary shell" of the small Haplozonaria, is quite different from the medullary shell of the larger Diplozonaria, and particularly of the well-known Tetrapyle. The former observers, J. Müller as well as R. Hertwig, have described in these forms also the medullary shell as a simple spherical or oblong body. But a careful comparison of many hundred specimens of them and of their dimensions, has convinced me that this was an error, and that the small spherical or elliptical medullary shell of Tetrapyle and the other Diplozonaria possesses already the same complex structure, composed of a system of three girdles, as Trizonium and Larnacilla. Whilst in the Haplozonaria probably the simple central chamber only represents the medullary shell (enclosed in the central capsule), and the first system of girdles (complete in Trizonium) the external cortical shell, with the progressive growth this latter becomes enclosed in the central capsule and so constitutes the "trizonal medullary shell" of the Diplozonaria and Triplozonaria.

A very difficult matter is the mode of connection between the cortical and medullary shell. In most of the Pylonida it seems that the first or transverse girdle (in each system) is produced by the formation of two lateral wings or chambers (one on each side of the medullary shell), so that each wing (or half girdle) represents a short and wide, nearly cylindrical tube, the axis of which (with free openings on both poles) is parallel to the principal axis of the medullary shell. In this case (probably the ordinary one) both principal faces of the medullary shell itself (dorsal and ventral face) constitute the middle part of the first girdle whilst its lateral parts are formed by the wings (comparable to the lateral chambers of Amphitholus).

In the second case (probably a much rarer one) there is a free ring-shaped space between the medullary shell and the first (transverse) girdle, and both are connected by a small number of very short and small radial beams (R. Hertwig, loc. cit., p. 52, line 19 to 21 from above). This mode of connection would be the same as is common between the concentric shells of the Sphæroidea and Prunoidea. The distinction between these two different modes of connection is often very difficult.

The second or lateral girdle is commonly not in direct connection with the medullary shell, or only by some scattered radial beams (mainly in the principal axis). This lateral guide arises by prolongation of both wings of the transverse girdle in the lateral plane, so that from both sides (right and left) they become united on the poles of the principal axis. The minor axis of the elliptical lateral ring (thus formed) is therefore the major axis of the foregoing (transverse) elliptical ring; the major axes of both are perpendicular one to another. The major axis of the lateral ring is the principal (or longitudinal) axis of the whole body.

The third or sagittal girdle becomes developed from the second almost in the same manner as the second from the first. On both poles of the principal axis two latticed wings arise from the lateral girdle, growing further in the direction of an elliptical ring, which represents the perimeter of the sagittal plane or median plane. These wings are already mentioned by J. Müller as "prominent roofs, protecting the gates of the Tetrapyle-shell." If these roofs grow towards the equatorial plane of the shell and become united in pairs on the poles of the sagittal axis, the third girdle becomes complete. R. Hertwig supposes that the minor axis of this sagittal girdle is constantly at the same time the major axis of the lateral girdle, but this is not always the case. Very often the size of both these girdles is nearly the same, or one is not much larger than the other. In this case the principal axis of the body is the major axis of the second as well as of the third girdle.

The characteristic "gates" of the Pylonida, or the large wide openings in their cortical shell, remaining between the crossed latticed girdles, are in general roundish, sometimes nearly circular, commonly more elliptical, kidney-shaped or semilunar, their special form varying much according to the different form of the girdles. The narrowest part of each girdle, or its "isthmus," in the case of the halves of the transverse girdle is commonly at their origin from the medullary shell, in the case of the halves of the lateral girdle at the poles of the principal axis, and in the case of the halves of the sagittal girdle at the poles of the sagittal axis. The number of the gates is quite constant in the different genera. If only one girdle (the transverse) be developed, we find only two large gates, between the two wings on the poles of the principal axis (in Monozonium, Amphipyle, Amphipylonium). In all other cases there are four gates (determining the original name "Tetrapyle"), as well if only two or if all three girdles be completed. If two girdles be complete (in Dizonium, Tetrapyle, Tetrapylonium) the four gates lie opposite in pairs on the sagittal faces (two anterior and two posterior gates), and are limited by the transverse and lateral girdles. If all three girdles be complete (in Trizonium, Pylonium, Pylozonium) the four gates lie opposite in pairs on the lateral faces (two dorsal and two ventral gates), and are limited by the sagittal and the transverse girdles. If we turn the shell through an angle of 90°, we have the same aspect as in the former group. A sagittal septum sometimes becomes developed, beginning with two polar beams, rising from the poles of the principal axis. If these polar beams become branched and connected with the middle part of the lateral girdle, we get a latticed vertical septum, which divides the four gates of Tetrapyle into eight gates, Octopyle.

The lattice-work of the Pylonida is commonly very variable and irregular, with roundish meshes of very unequal size, therefore without value in the determination of the species. Commonly the outside of the shell is thorny, and often distinguished by larger radial spines, symmetrically disposed. We can separate these into two groups; "dimensive" spines, lying in one of the three dimensive axes (principal, transverse, or sagittal), and "diagonal" spines, lying crossed in pairs in diagonal axes. Among these latter eight diagonal wing-spines, which arise from the lateral edges of the four gates, are particularly remarkable; they are not only characteristic of Tetrapyle octacantha, but also of a large number of other Pylonida, and form the starting-point for many specific forms.

The shell of the Pylonida is characterised by extraordinary variability and great inclination to individual abnormalities, formation of varieties and transitions into other families, hence derived, as Larnacida, Tholonida, Lithelida, &c.

The central capsule in all Pylonida, in which I could observe it, was a true lentellipsis (or a "triaxial ellipsoid" in the geometrical sense, with the three unequal isopolar axes of the "rhombic octahedron"). In the living Pylonida it is commonly coloured pink or scarlet. During growth its dimensions are probably more or less changed, and perhaps the axes alternate. Regarding the relation of the central capsule to the skeleton, we can distinguish two different groups, quite as in the nearly allied Larnacida. In the Haplozonaria (as also in the Larnacillida) the central capsule encloses only the central chamber and is enveloped by the first system of girdles, whereas in the Diplozonaria and Triplozonaria (as in the Larnacalpida) that "trizonal shell" becomes enclosed (as the "medullary shell") in the central capsule, which is now enveloped by the second system of girdles as the "cortical shell."

Synopsis of the Genera of Pylonida.

III. Subfamily Haplozonaria. One system of girdles. Medullary shell simple, spherical or lentelliptical; cortical shell simple, with one, two, or three girdles.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Cortical shell only with one latticed (transverse) girdle,			279. Monozonium.
		Cortical shell with two perfect girdles (transverse and lateral),			280. Dizonium.
		Cortical shell with three perfect girdles (transverse, lateral, and sagittal			281. Trizonium.
III. Subfamily Diplozonaria. Two systems of concentric girdles. Medullary shell trizonal, with three perfect girdles; cortical shell simple, with one, two or three girdles.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Cortical shell only with one perfect (transverse) girdle,			282. Amphipyle.
		Cortical shell with two perfect girdles (the transverse and lateral).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Four gates simple,	283. Tetrapyle.
				Four gates bisected by a sagittal septum,	284. Octopyle.
		Cortical shell with three perfect girdles (transverse, lateral, and sagittal),			285. Pylonium.
III. Subfamily Triplozonaria. Three systems of concentric girdles. Medullary shell trizonal, with three perfect girdles, quite as the inner cortical shell; outer cortical shell with one, two, or three girdles.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Outer cortical shell (third system) only with one perfect (transverse) girdle,			286. Amphipylonium.
		Outer cortical shell with two perfect girdles (transverse and lateral),			287. Tetrapylonium.
		Outer cortical shell with three perfect girdles (transverse, lateral, and sagittal),			288. Pylozonium.

Subfamily 1. Haplozonaria, Haeckel.

Definition.—Pylonida with one single system of fenestrated girdles (with one, two, or three girdles, lying in one lentelliptical face).

Genus 279. Monozonium,^[14] n. gen.

Definition.—Pylonida with simple, spherical or subspherical, central chamber, surrounded by one single (transverse) latticed girdle.

The genus Monozonium is the most simple and primitive of all Pylonida, and may be regarded as their common ancestral form; it may probably be derived phylogenetically either directly from Cenosphæra or from Lentellipsis, either by apposition of two imperfect lateral chambers, or by surrounding it with an equatorial latticed girdle. This transverse girdle is composed of three parts, the central chamber and two lateral wings, which represent two short hollow latticed tubes, the axes of which are parallel to the principal axis. On both principal sides (on the anterior and posterior faces) there are two large open gates as in Amphipyle. If we imagine the openings of the tube-shaped lateral wings closed by lattice-work, Monozonium becomes transformed into Tholartus, the most simple form of Tholonida. Probably in all Pylonida the ontogeny of the shell begins with the formation of a Monozonium.

Subgenus 1. Monozonaris, Haeckel.

Definition.—Shell smooth or rough, without radial spines or thorns.

1. Monozonium primordiale, n. sp.

Central chamber of the shell spherical, smooth, with three to four pores on the half equator. Both wings of the girdle of the same breadth, but of twice the length of the central chamber, with three to four longitudinal rows of pores. No radial spines.

Dimensions.—Diameter of the central chamber 0.02; breadth of the wings 0.02, length 0.04; pores and bars 0.003.

Habitat.—Pacific, central area, Station 271, surface.

2. Monozonium alatum, n. sp. (Pl. 9, fig. 1).

Central chamber of the shell lentelliptical, smooth, one and a half times as long as broad, with three to four pores on the half equator. Both wings of the girdle twice as broad, and somewhat longer than the central chamber, with five to six longitudinal rows of pores. No radial spines.

Dimensions.—Length of the central chamber 0.03, breadth 0.02; breadth of the wings 0.04, length 0.05; pores and bars 0.004.

Habitat.—North Pacific, Station 241, surface.

Subgenus 2. Monozonitis, Haeckel.

Definition.—Shell with radial spines or thorns, symmetrically disposed.

3. Monozonium pleurostylum, n. sp.

Central chamber spherical, smooth, with four to five pores on the half equator. Both wings of the girdle of the same breadth, but somewhat longer than the central chamber, with four to five longitudinal rows of pores. On the poles of the lateral axis two opposite strong conical spines (one in the middle of each wing).

Dimensions.—Diameter of the central chamber 0.025; breadth of the wings 0.025, length 0.03; pores and bars 0.005.

Habitat.—Pacific, central area, Station 265, surface.

4. Monozonium amphistylum, n. sp.

Central chamber lentelliptical, one and a half times as long as broad, with three to four pores on the half equator. Breadth and length of each wing somewhat greater than that of the central chamber. On the latter two strong conical spines, opposite on the poles of the principal or longitudinal axis.

Dimensions.—Length of the central chamber 0.03, breadth 0.02; breadth of the wings 0.025, length 0.04; pores and bars 0.004.

Habitat.—South Atlantic, Station 332, surface.

5. Monozonium staurostylum, n. sp.

Central chamber lentelliptical, one and a third times as long as broad, with four to five pores on the half equator. Both wings of the girdle have the same breadth, but one and a half times the length of the central chamber. Four conical radial spines, two opposite on the poles of the lateral, two on the poles of the principal axis.

Dimensions.—Length of the central chamber 0.028, breadth 0.021; breadth of the wings 0.02, length 0.04.

Habitat.—South Pacific, Station 295, surface.

Genus 280. Dizonium,^[15] n. gen.

Definition.—Pylonida with simple, spherical or subspherical, central chamber, surrounded by two crossed latticed girdles, one smaller (primary) transverse and one larger (secondary) lateral girdle.

The genus Dizonium differs from the preceding Monozonium in the possession of two crossed elliptical lattice-girdles. The smaller girdle, immediately surrounding the central chamber, is the transverse girdle (the single girdle of Monozonium). On the poles of its major axis (the transverse axis) it is connected with the larger girdle, the elliptical perimeter of which circumscribes the lateral plane. The minor axis of this latter is the major axis of the former. Between the two crossed girdles remain four larger openings or gates, quite as in Tetrapyle. But whilst in Tetrapyle the enclosed medullary shell is a trizonal Larnacilla-shell, here in Dizonium it is a simple spherical or lentelliptical chamber.

Subgenus 1. Dizonaris, Haeckel.

Definition.—Shell smooth or rough, without radial spines or thorns.

1. Dizonium circulare, n. sp.

Central chamber of the shell spherical, smooth, with four to five pores on the half equator. Lateral girdle circular, three times as broad as the former. Four gates semilunar, twice as broad as high. No radial spines.

Dimensions.—Diameter of the central chamber 0.02, of the lateral girdle 0.06; height of the gates 0.02, breadth 0.04.

Habitat.—Pacific, central area, Station 274, surface.

2. Dizonium ellipticum, n. sp.

Central chamber of the shell elliptical, smooth, with three to four pores on the half equator. Lateral girdle elliptical, three times as long and broad as the central chamber. Four gates kidney-shaped, twice as broad as high. No radial spines.

Dimensions.—Length of the central chamber 0.03, breadth 0.02; length of the lateral girdle 0.09, breadth 0.06; height of the gates 0.02, breadth 0.038.

Habitat.—South Pacific, Station 288, surface.

3. Dizonium transversum, n. sp.

Central chamber of the shell spherical, rough, with five to six pores on the half equator. Lateral girdle transverse-elliptical, so that its longer axis corresponds to the lateral axis of the transverse girdle, and equals four times the diameter of the central chamber. Four gates kidney-shaped, four times as broad as high. No radial spines.

Dimensions.—Diameter of the central chamber 0.02; length of the lateral girdle 0.05, breadth 0.08; height of the gates 0.01, breadth 0.04.

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

Subgenus 2. Dizonitis, Haeckel.

Definition.—Shell with radial spines or thorns, symmetrically disposed.

4. Dizonium pleuracanthum, n. sp. (Pl. 9, fig. 2).

Central chamber of the shell nearly spherical, smooth. Lateral girdle elliptical, one and a third times as long as broad, three times as long as the central chamber. Four gates transverse-elliptical, one and a half times as broad as high. Two conical spines, opposite on the poles of the lateral axis.

Dimensions.—Diameter of the central chamber 0.03; length of the lateral girdle 0.1, breadth 0.075; height of the gates 0.026, breadth 0.04.

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

5. Dizonium amphacanthum, n. sp.

Central chamber elliptical. Lateral girdle elliptical, twice as long as broad. Four gates heart-shaped, about as high as broad. Two conical spines, opposite on the poles of the principal axis.

Dimensions.—Length of the central chamber 0.03, breadth 0.02; length of the lateral girdle 0.1, breadth 0.05; height and breadth of the gates 0.03.

Habitat.—Pacific, central area, Station 270, depth 2925 fathoms.

6. Dizonium stauracanthum, n. sp. (Pl. 9, fig. 3).

Central chamber spherical. Lateral girdle elliptical, one and a third times as long as broad. Four gates elliptical, one and a half times as broad as high, halved by an axial beam (as in Octopyle). Four conical radial spines opposite in pairs, two on the poles of the principal, two on the poles of the transverse axis.

Dimensions.—Diameter of the central chamber 0.025; length of the lateral girdle 0.09, breadth 0.06; height of the gates 0.024, breadth 0.036.

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

7. Dizonium octacanthum, n. sp.

Central chamber spherical. Lateral girdle elliptical, one and a half times as long as broad. Four gates kidney-shaped, twice as broad as high. Eight radial spines, opposite in pairs in two crossed diagonal planes.

Dimensions.—Diameter of the central chamber 0.02; length of the lateral girdle 0.075, breadth 0.05; height of the gates 0.02, breadth 0.04.

Habitat.—Pacific, central area, Station 272, surface.

Genus 281. Trizonium,^[16] n. gen.

Definition.—Pylonida with simple, spherical or subspherical, central chamber, surrounded by three latticed girdles, one smaller (primary) transverse, one larger (secondary) lateral, and one (tertiary) sagittal girdle.

The genus Trizonium represents the most highly developed form of the Haplozonaria, with three complete elliptical latticed girdles, crossed at right angles and lying in the perimeter of the three dimensive planes. Commonly the first (transverse) girdle is the smallest, immediately connected with the spherical or lentelliptical central chamber. The minor axis of the second (lateral) girdle is identical with the major axis of the first girdle. The third (sagittal) girdle is either larger than both others, or intermediate between them. If the four gates between the girdles become afterwards closed by lattice-work, the "trizonal shell" of Trizonium passes over into the typical Larnacilla, the ancestral form of a great many Larcoidea.

Subgenus 1. Trizonaris, Haeckel.

Definition.—Shell smooth or rough, without radial spines or thorns.

1. Trizonium tricinctum, n. sp. (Pl. 9, fig. 4).

Central chamber of the shell elliptical. Lateral girdle elliptical, one and a half times as long as broad. Four gates kidney-shaped, one and a half times as broad as high. Ten to eleven pores on the half equator, fourteen to sixteen on the half meridian of the lentelliptical shell. No radial spines on the surface.

Dimensions.—Length of the central chamber 0.024, breadth 0.016; length of the lateral girdle 0.075, breadth 0.05; height of the four gates 0.026, breadth 0.04.

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

2. Trizonium constrictum, n. sp.

Central chamber elliptical. Lateral girdle violin-shaped, on both sides in the middle constricted, twice as long as broad. Four gates transverse-elliptical, twice as broad as high. Eight to nine pores on the half equator, twelve to thirteen on the half meridian. No radial spines.

Dimensions.—Length of the central chamber 0.03, breadth 0.02; length of the lateral girdle 0.09, breadth (in the middle) 0.045; height of the gates 0.022, breadth 0.044.

Habitat.—Pacific, central area, Station 263, surface.

3. Trizonium hexagonium, n. sp.

Central chamber spherical. Lateral girdle hexagonal, with parallel sides, twice as long as broad. Four gates triangular, twice as broad as high. Eleven to twelve pores on the half equator, sixteen to eighteen on the half meridian. No radial spines.

Dimensions.—Diameter of the central chamber 0.025; length of the lateral girdle 0.08, breadth 0.04; height of the gates 0.018, breadth 0.036.

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

4. Trizonium octogonium, n. sp.

Central chamber spherical. Lateral girdle octagonal; two lateral sides of the octagon twice as long as the two polar sides and the four diagonal sides. Four gates hexagonal, one and a half times as broad as high. Nine to ten pores on the half equator, twelve to fourteen on the half meridian. No radial spines.

Dimensions.—Diameter of the central chamber 0.02; length of the lateral girdle 0.01, breadth 0.07; height of the gates 0.04, breadth 0.06.

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

Subgenus 2. Trizonitis, Haeckel.

Definition.—Shell with radial spines or thorns, symmetrically disposed.

5. Trizonium pleurobelonium, n. sp.

Central chamber spherical. Lateral girdle elliptical, one and a third times as long as broad. Four gates nearly circular. Ten to eleven pores on the half equator, fifteen to sixteen on the half meridian. Two opposite conical spines on the poles of the lateral axis.

Dimensions.—Diameter of the central chamber 0.02; length of the lateral girdle 0.08, breadth 0.06; height and breadth of the gates 0.025.

Habitat.—South Atlantic, off Buenos Ayres, Station 323, depth 1900 fathoms.

6. Trizonium amphibelonium, n. sp.

? Echinosphæra datura, R. Hertwig (partim), 1879, Organismus d. Radiol., p. 54, Taf. iv. figs. 8, 8a.

Central chamber lentelliptical. Lateral girdle lanceolate, nearly one and a half times as long as broad. Four gates subtriangular. Eight to nine pores on the half equator, ten to twelve on the half meridian. Two opposite thin and long spines on the poles of the principal axis, numerous shorter radial spines on the whole surface. Possibly this species is identical with one of the three different Larcoidea which R. Hertwig has described as Echinosphæra datura. His fig. 8, Taf. iv., would be the aspect from the sagittal girdle.

Dimensions.—Length of the central chamber 0.04, breadth 0.025; length of the lateral girdle 0.11, breadth 0.08; height of the gates 0.03, breadth 0.04.

Habitat.—Mediterranean (Genoa), Haeckel, (Messina), R. Hertwig, surface; Tropical Atlantic, Station 348, surface.

7. Trizonium staurobelonium, n. sp.

Central chamber spherical, with two opposite polar beams. Lateral girdle elliptical, one and a half times as long as broad. Four gates transverse-elliptical, half as high as broad. Ten to eleven pores on the half equator, fourteen to fifteen on the half meridian. Four conical radial spines, two on the poles of the lateral, two on the poles of the principal axis.

Dimensions.—Diameter of the central chamber 0.02; length of the lateral girdle 0.075, breadth 0.05; height of the gates 0.014, breadth 0.028.

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

8. Trizonium hexabelonium, n. sp.

Central chamber elliptical. Lateral girdle hexagonal, one and a half times as long as broad. Four gates rhombic, two-thirds as high as broad. Eight to nine pores on the half equator, twelve to thirteen on the half meridian. Six radial spines in the lateral plane, opposite in pairs on the six corners of the lateral girdle (two principal and four diagonal).

Dimensions.—Length of the central chamber 0.024, breadth 0.018; length of the lateral girdle 0.06, breadth 0.04; height of the gates 0.02, breadth 0.03.

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

9. Trizonium octobelonium, n. sp.

Central chamber elliptical. Lateral girdle hexagonal, one and one-third times as long as broad. Four gates kidney-shaped or nearly rhombic, twice as broad as high. Eleven to twelve pores on the half equator, sixteen to seventeen on the half meridian. Eight radial spines, opposite in pairs in two crossed diagonal planes. (An intermediate stage between Dizonium octacanthum and Amphipyle octostyle.)

Dimensions.—Length of the central chamber 0.03, breadth 0.024; length of the lateral girdle 0.09, breadth 0.07; height of the gates 0.025, breadth 0.05.

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

10. Trizonium decabelonium, n. sp.

Central chamber elliptical. Lateral girdle hexagonal, one and a half times as long as broad. Four gates rhombic, twice as broad as high. Twelve to thirteen pores on the half equator, seventeen to eighteen on the half meridian. Ten radial spines, two opposite on the two poles of the principal axis, eight others opposite in pairs in two crossed diagonal planes.

Dimensions.—Length of the central chamber 0.04, breadth 0.03; length of the lateral girdle 0.12, breadth 0.08; height of the gates 0.03, breadth 0.06.

Habitat.—North Atlantic, Station 353, surface.

11. Trizonium dodecabelos, n. sp.

Central chamber spherical. Lateral girdle octagonal, nearly twice an long as broad. Four gates hexagonal, one and a half times as broad as high. Nine to ten pores on the half equator, fifteen to sixteen on the half meridian. Twelve radial spines, four in the lateral plane, in pairs on both sides of the poles of the principal axis, eight others opposite in pairs in two crossed diagonal axes.

Dimensions.—Diameter of the central chamber 0.025; length of the lateral girdle 0.1, breadth 0.06; height of the gates 0.033, breadth 0.05.

Habitat.—Pacific, central area, Station 272, surface.

Subfamily 2. Diplozonaria, Haeckel.

Definition.—Pylonida with two concentric systems of fenestrated girdles, lying in two concentric lentelliptical faces (every one system with one to three girdles, lying in one lentelliptical face).

Genus 282. Amphipyle,^[17] Haeckel, 1881, Prodromus, p. 463.

Definition.—Pylonida with trizonal lentelliptical medullary shell, surrounded by one single (transverse) latticed cortical girdle.

The genus Amphipyle opens the large series of Diplozonaria, comprising all Pylonida, the shell of which is composed of two concentric systems of latticed girdles; the first system constituting the characteristic "trizonal medullary shell" or "Larnacilla-shell;" the second system composed of one to three girdles of the second order. The first system lies inside, the second outside the central capsule. In Amphipyle only the first (transverse) girdle of the second system becomes developed, and therefore on both poles of the principal axis are two large open gates. Amphipyle repeats the two-winged form of Monozonium; but whilst the medullary shell in this latter is a simple central chamber, it is here a trizonal Larnacilla-shell.

Subgenus 1. Amphipylissa, Haeckel.

Definition.—Cortical shell smooth or thorny, but without large, symmetrically disposed spines.

1. Amphipyle aceros, n. sp.

Cortical shell quite smooth, without any spines or thorns. Both lateral wings (or opposite half girdles) semilunar, with convex lateral crest, three times as long as broad; twice as broad as the trizonal lentelliptical medullary shell.

Dimensions.—Length of the medullary shell 0.05, breadth 0.03; length of each lateral wing (or principal dimension of the latticed girdle) 0.18, breadth of it (or transverse dimension of each girdle-tube) 0.06.

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

2. Amphipyle stenoptera, n. sp.

Cortical shell smooth, without spines. Both lateral wings of the same breadth as the lentelliptical medullary shell, but five times as long as broad, prolonged on both ends into cylindrical latticed tubes, with rectilinear lateral crest.

Dimensions.—Length of the medullary shell 0.06, breadth 0.04; length of each cylindrical lateral wing 0.2, breadth 0.04.

Habitat.—South Atlantic, off Ascension Island, Station 343, surface.

3. Amphipyle platyptera, n. sp.

Cortical shell thorny, but without larger spines. Both lateral wings nearly triangular, very broad and short, four times as broad as the medullary shell between them, and only twice as long as broad, with rectilinear lateral crest.

Dimensions.—Length of the medullary shell 0.05, breadth 0.25; length of each lateral wing 0.18, breadth 0.09.

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

Subgenus 2. Amphipylura, Haeckel.

Definition.—Cortical shell armed with large, symmetrically disposed spines.

4. Amphipyle amphiceros, n. sp.

Cortical shell with two conical spines on the poles of the longitudinal axis (of the lentelliptical medullary shell), without other large spines, but with small thorns on the surface; two to three longitudinal rows of irregular, roundish pores on each half wing of the cortical girdle.

Dimensions.—Length of the medullary shell (or principal axis) 0.06, breadth (or transverse axis) 0.04; length of each lateral wing 0.2, breadth of it 0.05.

Habitat.—Western Tropical Pacific, Station 222, surface.

5. Amphipyle tetraceros, n. sp. (Pl. 9, fig. 5).

Cortical shell with smooth surface, and with four strong conical spines in the lateral plane, opposite in pairs on the ends of the concave lateral crests (one pair on the end-points of the lateral line of each wing); four to five longitudinal rows of irregular, roundish pores on each half wing of the cortical girdle. Surface of the medullary shell spiny.

Dimensions.—Length of the medullary shell 0.08, breadth of the same 0.05; length of each lateral wing 0.16, breadth 0.04.

Habitat.—Pacific, central area, Station 271, surface.

6. Amphipyle stauroceros, n. sp.

Cortical shell with four strong conical spines, two on the poles of the longitudinal axis, two opposite on the poles of the transverse axis (perpendicular to the former). Three to four longitudinal rows of irregular, roundish pores on each half wing of the cortical girdle, about six pores in the longest row. Lateral crest convex.

Dimensions.—Length of the medullary shell 0.05, breadth 0.03; length of each lateral wing 0.15, breadth 0.08.

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

7. Amphipyle amphiptera, n. sp. (Pl. 9, fig. 7).

Cortical shell with six strong conical spines, lying in the lateral plane in three parallel longitudinal lines; two on the poles of the longitudinal axis, two others on the poles of the wing axes, which are parallel to the former. Two to three longitudinal rows of irregular, roundish pores on each half wing of the cortical girdle, about eight pores in the longest row. Lateral crest convex, thorny.

Dimensions.—Length of the medullary shell 0.06, breadth 0.045; length of each lateral wing 0.09, breadth 0.035.

Habitat.—Western Tropical Pacific, Station 224, surface.

8. Amphipyle hexaceros, n. sp.

Cortical shell thorny, with six strong conical spines lying in the lateral plane; two on the poles of the lateral axis (in the central point of each wing), two on the end-points of the triangular crest of each wing (on both poles of the longitudinal wing-axis).

Dimensions.—Length of the medullary shell 0.06, breadth 0.04; length of each lateral wing 0.13, breadth 0.07.

Habitat.—South Pacific, Station 291, surface.

9. Amphipyle octoceros, n. sp.

Cortical shell thorny, with eight long radial spines, lying in two crossed diagonal planes, opposite in pairs. These eight horns are the prolongations of the anterior and posterior edges of each wing, on both sides of its lateral plane; they are of great importance, as appearing (by heredity) in many other Pylonida (e.g., in Tetrapyle octacantha). Lateral crest of each wing without spines, slightly convex.

Dimensions.—Length of the medullary shell 0.07, breadth 0.05; length of each lateral wing 0.15, breadth 0.06.

Habitat.—Pacific, central area, Stations 270 to 274, surface.

10. Amphipyle cladoceros, n. sp.

Cortical shell spiny, with eight strong ramified radial spines, lying in the same two crossed diagonal planes as in the preceding species. It differs from this in the ramification of the eight horns, which bear six to nine irregular lateral branches, partly simple, partly bifurcate. Lateral crest of each wing spiny, convex.

Dimensions.—Length of the medullary shell 0.06, breadth 0.045; length of each lateral wing (without spines) 0.2, breadth 0.09.

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

11. Amphipyle decaceros, n. sp.

Cortical shell spiny, with ten strong conical spines; eight lying in two crossed diagonal planes, in the same disposition (opposite in pairs) as in both preceding species; two others opposite on the poles of the principal axis, arising from both poles of the medullary shell (columella-beams). Spiny crest of the wings convex, semilunar.

Dimensions.—Length of the medullary shell 0.04, breadth 0.03; length of each lateral wing 0.12, breadth 0.04.

Habitat.—North Atlantic, Station 354, surface.

12. Amphipyle dodecaceros, n. sp.

Cortical shell thorny, with twelve large cylindrical spines; eight lying in two crossed diagonal planes, in the same disposition (opposite in pairs) as in the three preceding species; four others crossed at right angles in the lateral plane, two opposite on the poles of the principal, two on the poles of the lateral axis (the latter shorter). Both lateral wings nearly rhombic.

Dimensions.—Length of the medullary shell 0.06, breadth 0.04; length of the lateral wings 0.15, breadth 0.05.

Habitat.—South Atlantic, coast of Brazil, Rabbe, surface.

13. Amphipyle callizona, n. sp. (Pl. 9, fig. 6).

Cortical shell smooth, with sixteen strong and short conical spines, lying opposite in pairs in two crossed diagonal planes; each lateral wing four-sided prismatic, its lateral face concave, both ends truncated, and each end provided with four divergent spines. Length of the wings somewhat greater, but breadth smaller, than that of the medullary shell.

Dimensions.—Length of the medullary shell 0.07, breadth 0.05; length of the lateral wings 0.09, breadth 0.03.

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

Genus 283. Tetrapyle,^[18] J. Müller, 1858, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 154.

Definition.—Pylonida with trizonal lentelliptical medullary shell, surrounded by two crossed latticed cortical girdles, one smaller (primary) transverse, and one larger (secondary) lateral girdle. Four gates between the two cortical girdles simple, without a sagittal septum.

The genus Tetrapyle, till 1881 the only known genus of the whole family, was founded by Johannes Müller in 1858, and clearly illustrated by the Mediterranean (and common cosmopolitan) Tetrapyle octacantha, hitherto the best known type of this family. Afterwards (1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 832) Ehrenberg founded the genus Schizomma for a nearly allied form, which exhibits only slight specific differences (compare my Monograph, 1862, p. 434). Some good remarks on the structure of this typical genus and its relations to other Pylonida are to be found in Richard Hertwig's Organismus, &c., 1879, p. 52, but the true trizonal structure of the medullary shell in this genus was not recognised by him, so that his description agrees more with Dizonium. We confine here the genus Tetrapyle to those Pylonida for which Tetrapyle octacantha of J. Müller remains the determining type; the cortical shell is composed only of two perfect lattice-girdles (the transverse and lateral), between which four wide gates remain open. This structure is similar to that of Dizonium; but whilst here the medullary shell is a simple central chamber, in Tetrapyle it is a complete trizonal or Larnacilla-shell.

Subgenus 1. Tetrapylissa, Haeckel.

Definition.—Cortical shell smooth or thorny, but without large, symmetrically disposed spines.

1. Tetrapyle circularis, n. sp. (Pl. 9, fig. 8).

Cortical shell rough, without radial spines. Lateral girdle circular, therefore the longitudinal axis is equal to the transverse. Four gates kidney-shaped, twice as broad as high. In each half wing of the transverse girdle six to seven longitudinal rows of irregular, roundish pores.

Dimensions.—Medullary shell 0.05 long, 0.04 broad; cortical shell 0.15 long and broad; gates 0.04 high, 0.08 broad.

Habitat.—Pacific, central area, Station 263, surface.

2. Tetrapyle circopyle, n. sp.

Cortical shell smooth, without radial spines. Lateral girdle elliptical, one and a half times as long as broad. Four gates nearly circular. On each half wing of the transverse girdle four to five rows of subregular, circular pores. (Similar to Tetrapyle pleuracantha, Pl. 9, fig. 9, but without lateral spines.)

Dimensions.—Medullary shell 0.04 long, 0.03 broad; cortical shell 0.16 long, 0.11 broad; gates 0.05 high and broad.

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

3. Tetrapyle quadriloba, Haeckel.

Tetrapyle quadriloba, Haeckel, 1862, Monogr. d. Radiol., p. 436. Schizomma quadrilobum, Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 815; Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, Taf. x. figs. 12-14.

Cortical shell thorny, without regular, radial spines. Lateral girdle elliptical, one and a half times as long as broad. Four gates nearly circular. On each half wing of the transverse girdle three to four rows of irregular, roundish pores.

Dimensions.—Medullary shell 0.06 long, 0.04 broad; cortical shell 0.16 long, 0.1 broad; diameter of the gates 0.05.

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

4. Tetrapyle nephropyle, n. sp.

Cortical shell thorny, without radial spines. Lateral girdle elliptical, one and a third times as long as broad. Four gates kidney-shaped, nearly twice as broad as high, with two prominent polar spines on the poles of the longitudinal axis of the medullary shell. On each half wing of the transverse girdle three to four longitudinal rows of large roundish pores.

Dimensions.—Medullary shell 0.06 long, 0.04 broad; cortical shell 0.24 long, 0.18 broad; gates 0.05 high, 0.08 broad.

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

5. Tetrapyle cardiopyle, n. sp.

Cortical shell rough, without radial spines. Lateral girdle with hexagonal contour, nearly cylindrical in the middle part, conical at both ends, twice as long as broad. Four gates heart-shaped, about as high as broad. On each half wing of the transverse girdle three to four longitudinal rows of subregular, polygonal pores.

Dimensions.—Medullary shell 0.04 long, 0.02 broad; cortical shell 0.14 long, 0.07 broad; gates 0.05 high and broad.

Habitat.—Eastern Tropical Atlantic, Station 348, depth (2450) fathoms.

Subgenus 2. Tetrapylura, Haeckel.

Definition.—Cortical shell armed with large, symmetrically disposed spines.

6. Tetrapyle fusiformis, n. sp.

Cortical shell rough, with two strong conical spines on the poles of the longitudinal axis. Lateral girdle spindle-shaped, one and a half times as long as broad. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle four to five longitudinal rows of irregular, roundish pores.

Dimensions.—Medullary shell 0.07 long, 0.05 broad; cortical shell 0.18 long, 0.12 broad; gates 0.04 high, 0.08 broad.

Habitat.—Western Tropical Atlantic, Mexican Gulf Stream, depth 1500 fathoms, Schaffner.

7. Tetrapyle pleuracantha, n. sp. (Pl. 9, fig. 9).

Cortical shell rough, with two strong conical spines on the poles of the transverse axis. Lateral girdle elliptical, one and half times as long as broad. Four gates subcircular or nearly hexagonal, about as high as broad. On each half wing of the transverse girdle three to four longitudinal rows of very irregular pores.

Dimensions.—Medullary shell 0.045 long, 0.035 broad; cortical shell 0.16 long, 0.11 broad; gates 0.045 high and broad.

Habitat.—Western Tropical Pacific, off New Guinea, Stations 222 to 224, depths 1850 to 2450 fathoms.

8. Tetrapyle transversa, n. sp.

Cortical shell thorny, with two strong conical lateral spines on the poles of the transverse axis. Lateral girdle elliptical, only four-fifths as long as broad. Four gates elliptical, twice as broad as high, with two prominent spines on the poles of the longitudinal axis of the medullary shell. On each half wing of the transverse girdle five to six longitudinal rows of subregular, roundish pores. (Similar to Octopyle transversa, but without sagittal septum and with stronger lateral spines.)

Dimensions.—Medullary shell 0.05 long, 0.035 broad; cortical shell 0.12 long, 0.15 broad; gates 0.03 high, 0.06 broad.

Habitat.—Southern Pacific, Station 290, surface.

9. Tetrapyle cruciata, n. sp.

Cortical shell smooth, with four strong radial spines, two on the poles of the longitudinal axis, two on the poles of the transverse axis. Lateral girdle nearly circular, quite as long as broad. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle five to six rows of subregular, circular pores.

Dimensions.—Medullary shell 0.06 long, 0.05 broad; cortical shell 0.16 long and broad; gates 0.05 high, 0.09 broad.

Habitat.—South Atlantic, Station 330, surface.

10. Tetrapyle staurophora, n. sp.

Cortical shell thorny, with four strong radial spines, two on the poles of the longitudinal axis, two on the poles of the transverse axis. Lateral girdle elliptical, one and a half times as long as broad. Four gates nearly hexagonal, quite as high as broad. On each half wing of the transverse girdle three to four longitudinal rows of irregular, roundish pores.

Dimensions.—Medullary shell 0.06 long, 0.04 broad; cortical shell 0.18 long, 0.12 broad; gates 0.08 high and broad.

Habitat.—Western Tropical Atlantic, coast of Brazil, Rabbe, surface.

11. Tetrapyle quadricornis, n. sp.

Cortical shell thorny, with four strong horn-like curved spines, lying in the lateral plane and converging in pairs towards the poles of the transverse axis. Lateral girdle elliptical, one and a third times as long as broad. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle four to five rows of irregular, roundish pores. (May be only the young form of Pylonium quadricorne, Pl. 9, fig. 14.)

Dimensions.—Medullary shell 0.05 long, 0.04 broad; cortical shell 0.16 long, 0.12 broad; gates 0.03 high, 0.07 broad.

Habitat.—Pacific, central area, Stations 270 to 274, surface.

12. Tetrapyle tetracantha, n. sp.

Cortical shell thorny, with four strong radial spines lying in the lateral plane and in pairs in its two crossed diagonal axes. Lateral girdle elliptical, constricted in the middle, nearly twice as long as broad. Four gates kidney-shaped, one and a half times as broad as high. On each half wing of the transverse girdle three to four longitudinal rows of large, irregular, roundish pores. (Similar to Tetrapylonium quadrangulare, Pl. 49, fig. 15, but without a sagittal girdle and with stronger lateral spines.)

Dimensions.—Medullary shell 0.06 long, 0.04 broad; cortical shell 0.18 long, 0.1 broad; gates 0.007 high, 0.01 broad.

Habitat.—North Atlantic, Canary Islands, Station 353, surface.

13. Tetrapyle quadrigata, n. sp.

Cortical shell thorny, with four brush-like groups of radial spines on the four diagonal corners of the lateral plane, opposite in pairs in diagonal axes. Lateral girdle nearly square, somewhat broader than long. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle five to six longitudinal rows of irregular, roundish pores.

Dimensions.—Medullary shell 0.06 long, 0.04 broad; cortical shell 0.14 long, 0.15 broad; gates 0.03 high, 0.07 broad.

Habitat.—Pacific, central area, Station 270, surface.

14. Tetrapyle octacantha, J. Müller.

Tetrapyle octacantha, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 33, Taf. ii. figs. 1-6.

Tetrapyle octacantha, Haeckel, 1862, Monogr. d. Radiol., p. 435.

Tetrapyle octacantha, R. Hertwig, 1879, Organismus d. Radiol., p. 52, Taf. iv. fig. 7, Taf. vi. figs. 2, 5, 5a.

Cortical shell thorny, with eight long and thin, cylindrical radial spines, lying in two crossed diagonal planes, opposite in pairs. These eight characteristic diagonal spines (or "angular spines") are the same as in Amphipyle octoceros and many other Pylonida, and arise as prolongations of the proximal edges of the four gates (or of the lateral wings on the eight points, where they are intersected by the edges of the lateral ring). This cosmopolitan, widely distributed and very variable species was a long time the only known species of all the Pylonida, and very accurately first described (1858) by Johannes Müller, afterwards (1879) by R. Hertwig. But in the descriptions of these authors also some different species (such as the following) may be confounded with the true typical Tetrapyle octacantha. The four gates of this species are transverse-elliptical or almost triangular, nearly twice as broad as high.

Dimensions.—Length of the medullary shell 0.04, breadth 0.03; length of the cortical shell 0.18, breadth 0.13; height of the gates 0.05, breadth 0.08.

Habitat.—Cosmopolitan; very common in all warmer seas, Mediterranean, Atlantic, Indian, Pacific, surface.

15. Tetrapyle cladacantha, n. sp.

Cortical shell thorny, with eight strong ramified radial spines, lying opposite in pairs in two crossed diagonal planes, as in the preceding species. It differs from this by the peculiar ramification of the eight spines, which bear two to eight simple or furcate lateral branches arising under right angles (already commencing in a transitional variety of Tetrapyle octacantha, J. Müller, loc. cit., Taf. ii. figs. 5, 6). Four gates transverse-elliptical, one and a half times as broad as high.

Dimensions.—Medullary shell 0.05 long, 0.04 broad; cortical shell 0.16 long, 0.13 broad; gates 0.05 high, 0.08 broad.

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

16. Tetrapyle pluteus, Haeckel.

Tetrapyle octacantha, var., J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. iii. figs. 7-12.

Cortical shell thorny, with eight strong radial spines, lying opposite in pairs, as in the two foregoing species. On the distal edge each of the four triangular gates is protected by a prominent roof of lattice-work (or "pluteus"), which arises from the distal part of the lateral girdle and connects the two angular diagonal spines of each gate. Therefore the shell assumes the characteristic form very well represented by J. Müller in his fig. 11 (seen from the lateral side) and fig. 7 (seen from the pole of the principal axis).

Dimensions.—Medullary shell 0.04 long, 0.03 broad; cortical shell 0.15 long, 0.11 broad; gates 0.045 high, 0.07 broad.

Habitat.—Mediterranean, Atlantic, Stations 348 to 353, &c., surface.

17. Tetrapyle turrita, n. sp. (Pl. 9, fig. 10).

Cortical shell smooth, but with ten strong conical spines, two on the poles of the principal axis, eight others symmetrically distributed on both sides of the distal edge of the four roundish gates, and directed towards the transverse axis. Lateral girdle lanceolate, twice as long as broad.

Dimensions.—Medullary shell 0.05 long, 0.04 broad; cortical shell 0.2 long, 0.1 broad; gates 0.05 high, 0.07 broad.

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

18. Tetrapyle dodecaceros, n. sp.

Cortical shell thorny, with twelve stronger conical spines, eight diagonal spines in two crossed planes (as in Tetrapyle octacantha), and four others in the lateral plane, in pairs on both sides of a deep sagittal constriction of the quadrangular lateral girdle. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle five to six longitudinal rows of irregular, roundish pores.

Dimensions.—Medullary shell 0.06 long, 0.04 broad; cortical shell 0.18 long, 0.14 broad; gates 0.04 high, 0.08 broad.

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

Genus 284. Octopyle,^[19] Haeckel, 1881, Prodromus, p. 464.

Definition.—Pylonida with trizonal lentelliptical medullary shell, surrounded by two crossed, latticed, cortical girdles; one smaller (primary) transverse, and one larger (secondary) lateral girdle. Four gates between the two cortical girdles divided by a sagittal septum into eight gates.

The genus Octopyle comprises those Pylonida which are distinguished from the nearly allied Tetrapyle by the development of a sagittal septum, dividing the four gates of the latter into eight separate gates. The septum begins with the formation of two axial rods or columellæ, which afterwards become branched; the branches communicating one with another and with the middle parts of the lateral girdle (on the poles of the principal axis), there is formed a latticed septum in the sagittal plane, which separates more or less incompletely the right and left halves of the shell. The four gates of Tetrapyle become halved by this septum, and their number doubled.

Subgenus 1. Octopylissa, Haeckel.

Definition.—Cortical shell smooth or thorny, but without larger symmetrically disposed spines.

1. Octopyle ovulina, n. sp.

Cortical shell lentelliptical, smooth, without thorns. Lateral girdle elliptical, one and a third times as long as broad. Transverse girdle narrow, with two pores on the isthmus (or on the narrowest part of each quadrant). Sagittal septum as long as the elliptical medullary shell. Eight gates egg-shaped.

Dimensions.—Length of the medullary shell 0.05, breadth 0.035; length of the cortical shell 0.16, breadth 0.12.

Habitat.—Pacific, central area, Station 274, surface.

2. Octopyle quadrata, n. sp.

Cortical shell thorny, nearly square, of equal length and breadth. Lateral girdle quadrangular, with rounded edges, of equal length and breadth. Transverse girdle narrow, with three pores on the isthmus. Sagittal septum of the same length as the subspherical medullary shell. Eight gates nearly circular.

Dimensions.—Diameter of the medullary shell 0.04, of the cortical shell 0.14.

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

3. Octopyle subglobosa, n. sp.

Cortical shell nearly spherical, thorny, of equal length and breadth. Lateral girdle broad, nearly circular. Transverse girdle broad, with four pores on the isthmus. Sagittal septum shorter than the subspherical medullary shell. Eight gates egg-shaped.

Dimensions.—Diameter of the medullary shell 0.05, of the cortical shell 0.13.

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

4. Octopyle transversaria, n. sp.

Cortical shell thorny, transverse-elliptical. Lateral girdle very broad, one and a third times as broad as long. Transverse girdle also very broad, with five pores on the isthmus. Sagittal septum shorter than the elliptical medullary shell. Eight gates small, roundish.

Dimensions.—Length of the medullary shell 0.05, breadth 0.04; length of the cortical shell 0.11, breadth 0.15.

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

Subgenus 2. Octopylura, Haeckel.

Definition.—Cortical shell armed with large, symmetrically disposed spines.

5. Octopyle amphistyle, n. sp.

Cortical shell smooth, nearly spindle-shaped, about twice as long as broad. Transverse girdle broad, with four large pores on the isthmus. Lateral girdle lanceolate. Sagittal septa about as long as the medullary shell, prolonged at both poles of the principal axis into two opposite, strong, angular spines. Eight gates obliquely quadrangular.

Dimensions.—Length of the medullary shell 0.07, breadth 0.05; length of the cortical shell 0.2, breadth 0.12.

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

6. Octopyle staurostyle, n. sp.

Cortical shell nearly rhombic, smooth, one and a half times as long as broad, with four strong, conical, radial spines, two on the poles of the principal axis (as prolongations of the sagittal septa), two others on the poles of the transverse axis. Transverse girdle narrow, with two pores on the isthmus. Sagittal septa longer than the medullary shell. Eight gates triangular.

Dimensions.—Length of the medullary shell 0.04, breadth 0.03; length of the cortical shell 0.18, breadth 0.12.

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

7. Octopyle tetrastyle, n. sp.

Cortical shell lentelliptical, with rough surface and four angular radial spines in the lateral plane, opposite in pairs in two crossed diagonals. Lateral girdle nearly rectangular (each angle with one spine), one and a third times as long as broad. Sagittal septum longer than the hexagonal medullary shell. Eight gates egg-shaped.

Dimensions.—Length of the medullary shell 0.05, breadth 0.03; length of the cortical shell 0.16, breadth 0.12.

Habitat.—North Atlantic, Station 354, surface.

8. Octopyle tetraptera, n. sp.

Cortical shell quadrangular, with thorny surface and four latticed wing-like prolongations on the corners of the quadrangle, opposite in pairs in two crossed diagonals, each wing supported by a strong radial spine. Lateral girdle quadrangular, one and a half times as long as broad. On the isthmus of the transverse girdle four pores. Sagittal septum longer than the hexagonal medullary shell. Eight gates triangular.

Dimensions.—Length of the medullary shell 0.07, breadth 0.04; length of the cortical shell 0.24, breadth 0.16.

Habitat.—Pacific, central area, Station 271, surface.

9. Octopyle stenozona, n. sp. (Pl. 9, fig. 11).

Cortical shell quadrangular, with thorny surface, and four conical spines in the lateral plane, on the points, where both cortical girdles are crossed. Lateral girdle very narrow, nearly square, with rounded corners, of equal length and breadth. On the isthmus of the narrow transverse girdle only one pore. Sagittal septum of the same length as the subspherical medullary shell. Eight gates irregular roundish or nearly circular.

Dimensions.—Diameter of the medullary shell 0.04, of the cortical shell 0.14.

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

10. Octopyle euryzona, n. sp.

Cortical shell nearly quadrangular, very thorny, with four bunches of stronger radial spines on the four corners. Lateral girdle broad, with rounded edges of the quadrangle, little longer than broad. On the isthmus of the broad transverse girdle four pores. Sagittal septum of the same length as the elliptical medullary shell, with many radial beams. Eight gates nearly square.

Dimensions.—Length of the medullary shell 0.05, breadth 0.035; length of the cortical shell 0.16, breadth 0.14.

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

11. Octopyle hexastyle, n. sp.

Cortical shell nearly rectangular, thorny, with six strong radial spines in the lateral plane, two opposite on the poles of the principal axis (prolongations of the principal beam at the sagittal septum), four others on the truncate corners of the quadrangular lateral girdle, which is one and a half times as long as broad. On the isthmus of the broad transverse girdle three pores. Sagittal septum longer than the hexagonal medullary shell. Eight egg-shaped gates.

Dimensions.—Length of the medullary shell 0.05, breadth 0.04; length of the cortical shell 0.18, breadth 0.12.

Habitat.—Northern Atlantic, surface; Canary Islands, Station 9, depth 3150 fathoms.

12. Octopyle sexangulata, n. sp. (Pl. 9, fig. 12).

Cortical shell thorny, hexagonal, with six strong conical radial spines on the six corners of the lateral girdle, lying in the lateral plane, two opposite on the poles of the transverse axis, four others in pairs on both sides of the annular sagittal constriction, which is only twice as long as the elliptical medullary shell. Transverse girdle broad, with five pores on the isthmus. Eight gates roundish, smaller than the medullary shell.

Dimensions.—Length of the medullary shell 0.045, breadth 0.035; length of the cortical shell 0.11, breadth 0.13.

Habitat.—Pacific, central area, Station 270, surface.

13. Octopyle octostyle, n. sp.

Cortical shell elliptical, thorny, with eight long cylindrical radial spines, lying in two crossed diagonal planes, opposite in pairs, quite as in the nearly related Tetrapyle octacantha. It differs from this species by the perfect, latticed, vertical sagittal septum, which divides every gate into two triangular halves. Lateral girdle elliptical, one and a third times as long as broad. Transverse girdle on the isthmus with three pores. Septum longer than the elliptical medullary shell.

Dimensions.—Length of the medullary shell 0.06, breadth 0.045; length of the cortical shell 0.16, breadth 0.12.

Habitat.—South Pacific, Station 288, surface.

14. Octopyle obtecta, n. sp.

Cortical shell quadrangular, thorny, with eight strong diagonal spines, lying in two crossed planes, and arising from the proximal edges of the gates in the same way as in the foregoing species. It differs from this by four prominent latticed roofs, which arise from the distal edge of the gates and connect the diagonal spines of one gate. Octopyle obtecta bears therefore the same relation to Octopyle octostyle that Tetrapyle pluteus does to Tetrapyle octacantha.

Dimensions.—Length of the medullary shell 0.055, breadth 0.04; length of the cortical shell 0.16, breadth 0.12.

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

15. Octopyle decastyle, n. sp. (Pl. 9, fig. 13).

Cortical shell thorny, nearly quadrangular, with ten stronger radial spines, two opposite on the poles of the principal axis (as prolongations of the axial beams), eight others opposite in pairs in two diagonal planes (as in the foregoing species). Lateral girdle nearly square, with slightly convex lateral faces, slightly concave principal faces. Transverse girdle broad, with four pores on the isthmus. Sagittal septum of the same length as the hexagonal medullary shell. Eight gates elliptical or irregular roundish.

Dimensions.—Length of the medullary shell 0.05, breadth 0.032; diameter of the cortical shell 0.15.

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

Genus 285. Pylonium,^[20] Haeckel, 1881, Prodromus, p. 464.

Definition.—Pylonida with trizonal lentelliptical medullary shell surrounded by three crossed latticed cortical girdles, one smaller (primary) transverse, one larger (secondary) lateral, and one (tertiary) sagittal girdle.

The genus Pylonium is the most highly developed among the Diplozonaria, with six complete latticed girdles, three on the medullary shell, three on the cortical shell, the latter corresponding to the former. In each of the two systems the transverse girdle is smaller than the lateral; the sagittal girdle may be smaller or larger than the lateral girdle. Pylonium repeats the typical form of Trizonium; but whilst in this latter the medullary centre of the shell is a simple spherical chamber, here in Pylonium it is a true trizonal or Larnacilla-shaped medullary shell.

Subgenus 1. Pylonissa, Haeckel.

Definition.—Cortical shell smooth or thorny, but without large, symmetrically disposed spines.

1. Pylonium circozonium, n. sp.

Cortical shell thorny, without radial spines; all its three girdles nearly of the same size, subcircular, very narrow, only with one to two rows of pores. Four gates subcircular.

Dimensions.—Principal axis 0.12, transverse axis 0.11; diameter of the subspherical medullary shell 0.05.

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

2. Pylonium hexazonium, n. sp.

Cortical shell smooth, without symmetrical radial spines. Transverse girdle elliptical, one and a half times as long as broad. Lateral and sagittal girdles nearly circular. Four gates egg-shaped.

Dimensions.—Principal axis 0.16, transverse axis 0.15; diameter of the subspherical medullary shell 0.04.

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

3. Pylonium nephropylium, n. sp.

Cortical shell thorny, without radial spines. All its three girdles elliptical, one and a third times as long as broad. Four gates kidney-shaped, nearly twice as broad as high.

Dimensions.—Principal axis 0.17, transverse axis 0.13; length of the lentelliptical medullary shell 0.04, breadth 0.03.

Habitat.—Pacific, central area, Station 273, depth 2350 fathoms.

Subgenus 2. Pylonura, Haeckel.

Definition.—Cortical shell armed with large, symmetrically disposed spines.

4. Pylonium quadricorne, n. sp. (Pl. 9, fig. 14).

Cortical shell thorny, with four strong horn-like curved spines in the lateral plane. All its three girdles elliptical, one and a third times as long as broad. Four gates kidney-shaped, twice as broad as high. (This species is a further developmental stage of Tetrapyle quadricornis, with perfect sagittal girdle.)

Dimensions.—Principal axis 0.16, transverse axis 0.12; length of the medullary shell 0.05, breadth 0.04.

Habitat.—Pacific, central area, Stations 270 to 274, surface; Indian Ocean, Madagascar, Rabbe, surface.

5. Pylonium octacanthum, n. sp.

Cortical shell thorny, with eight long and thin cylindrical radial spines, lying in two crossed diagonal planes, opposite in pairs, and arising from the eight points where the transverse girdle is crossed by the lateral girdle. All three girdles elliptical, one and a half times as long as broad; four gates triangular. (This species is a further developmental stage of Tetrapyle octacantha, with perfect sagittal girdle.)

Dimensions.—Principal axis 0.18, transverse axis 0.13; length of the medullary shell 0.03 to 0.04.

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

6. Pylonium stenozonium, n. sp.

Cortical shell thorny, with eight short conical radial spines, lying in two crossed diagonal planes (as in the foregoing species). All three girdles nearly of the same size, subcircular, very narrow, only with one to two rows of pores. Four gates kidney-shaped.

Dimensions.—Principal axis 0.15, transverse axis 0.14; diameter of the quadrangular medullary shell 0.04.

Habitat.—Equatorial Atlantic, Station 347, surface.

Subfamily 3. Triplozonaria, Haeckel.

Definition.—Pylonida with three concentric systems of fenestrated girdles, lying in three concentric lentelliptical faces (every system with one to three girdles lying in one lentelliptical face).

Genus 286. Amphipylonium,^[21] Haeckel, 1881, Prodromus, p. 463.

Definition.—Pylonida with trizonal lentelliptical medullary shell, surrounded by a double latticed cortical shell; inner cortical shell Pylonium-shaped, with three perfect crossed girdles; outer cortical shell only represented by a single (transverse) girdle.

The genus Amphipylonium opens the series of Triplozonaria, or of those Pylonida in which the shell is composed of three concentric systems of latticed girdles. The first (and innermost) system represents the complete trizonal medullary shell, which is probably a lentelliptical Larnacilla-shell. The first and intermediate system is formed of a complete trizonal cortical shell of the same form, but much larger (like Pylonium). The third (and outermost) system is represented by one to three latticed girdles, corresponding to the former and forming an outer or second cortical shell. In Amphipylonium (as the most simple form of the Triplozonaria) there is only developed the first (transverse) girdle of the third system. It repeats therefore the form of Amphipyle, the cortical shell of which is here double (Prodromus, 1881, p. 463).

1. Amphipylonium semilunare, n. sp.

Inner cortical shell lentelliptical, one and a half times as long as broad, with smooth surface and four semilunar gates. Transverse girdle of the outer cortical shell with two smooth semilunar wings, with convex, smooth lateral crests; each wing as broad as the transverse girdle of the inner cortical shell and twice as long as its lateral girdle.

Dimensions.—Length of the lentelliptical medullary shell 0.04, breadth 0.03; length of the inner cortical shell 0.15, breadth 0.1; length of each lateral wing of the outer cortical shell 0.3, breadth 0.1.

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

2. Amphipylonium spinosissimum, n. sp.

Inner cortical shell lentelliptical, one and a third times as long as broad, with thorny surface and four kidney-shaped gates. Transverse girdle of the outer cortical shell very spiny, with two semilunar wings, with convex thorny lateral crests; each wing one and a half times as broad as the transverse girdle of the inner cortical shell, and one and a half times as long as its lateral girdle.

Dimensions.—Length of the lentelliptical medullary shell 0.05, breadth 0.03; length of the inner cortical shell 0.16, breadth 0.12; length of each lateral wing of the outer cortical shell 0.24, breadth 0.18.

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

3. Amphipylonium tetraceros, n. sp.

Inner cortical shell hexagonal, one and a half times as long as broad, with smooth surface and four transverse elliptical gates. Transverse girdle of the outer cortical shell smooth, with rectilinear smooth lateral crests, which are prolonged at both ends into strong conical spines (therefore four spines in the lateral plane); each wing of the same breadth as the transverse girdle of the inner cortical shell, and twice as long as its lateral girdle.

Dimensions.—Length of the hexagonal medullary shell 0.03, breadth 0.02; length of the inner cortical shell 0.12, breadth 0.08; length of each lateral wing of the outer cortical shell 0.24, breadth 0.08.

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

4. Amphipylonium octoceros, n. sp.

Inner cortical shell quadrangular, one and a third times as long as broad, with thorny surface and four kidney-shaped gates. Transverse girdle of the outer cortical shell thorny, constricted at the equator, with concave thorny lateral crests, and with eight strong radial spines, opposite in pairs and lying in two crossed diagonal planes; each wing narrower than the transverse girdle of the inner cortical shell and twice as long as its lateral girdle.

Dimensions.—Length of the subspherical medullary shell 0.04, breadth 0.035; length of the inner cortical shell 0.14, breadth 0.11; length of each lateral wing of the outer cortical shell 0.26, breadth 0.09.

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

Genus 267. Tetrapylonium,^[22] Haeckel, 1881, Prodromus, p. 464.

Definition.—Pylonida with trizonal lentelliptical medullary shell, surrounded by a double latticed cortical shell; inner cortical shell Pylonium-shaped, with three perfect crossed girdles; outer cortical shell represented by two crossed girdles, one (smaller) transverse and one (larger) lateral girdle.

The genus Tetrapylonium represents a further developmental stage of the foregoing Amphipylonium; whilst in this latter the outer cortical shell (or the third system of girdles) is formed only by a transverse girdle, here this is crossed by a lateral girdle. Tetrapylonium repeats therefore the typical form of Tetrapyle, but with doubled cortical shell (Prodromus, 1881, p. 464).

1. Tetrapylonium pantellipticum, n. sp.

Outer cortical shell elliptical, one and a third times as long as broad, with smooth surface and four elliptical gates. Inner cortical shell elliptical, with smooth surface and four elliptical gates which repeat the form of the four outer gates, but are of half the size. Transverse girdle broad, with five pores on the isthmus.

Dimensions.—Length (or principal axis) of the first shell (medullary shell) 0.04, breadth (or transverse axis) 0.03; length of the second (or inner cortical) shell 0.12, breadth 0.09; length of the third (or outer cortical) shell 0.18, breadth 0.14.

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

2. Tetrapylonium reniforme, n. sp.

Outer cortical shell elliptical, one and a half times as long as broad, with thorny surface and four large kidney-shaped gates. Inner cortical shell of the same form, but one-third smaller, also with four kidney-shaped gates. Transverse girdle small, but with two pores on the isthmus.

Dimensions.—Length of the first (innermost) shell 0.03, breadth 0.02; length of the second (middle) shell 0.14, breadth 0.08; length of the third (outermost) shell 0.2, breadth 0.11.

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

3. Tetrapylonium quadrangulare, n. sp. (Pl. 9, fig. 15).

Outer cortical shell nearly quadrangular, one and a third times as long as broad, with four rounded corners, from which arise in the lateral plane four three-sided pyramidal radial spines, opposite in pairs in two crossed diagonal axes. Surface thorny; four gates elliptical or nearly quadrangular. Inner cortical shell more elliptical, by one half smaller, with broader transverse girdle and four kidney-shaped gates. Medullary shell nearly spherical, of half the size.

Dimensions.—Length of the first shell 0.045, breadth 0.035; length of the second shell 0.1, breadth 0.07; length of the third shell 0.16, breadth 0.11.

Habitat.—South Atlantic, off Tristan da Cunha, Station 332, depth 2200 fathoms.

4. Tetrapylonium octacanthum, n. sp.

Outer cortical shell elliptical, one and a third times as long as broad, with thorny surface, and eight long and thin radial spines arising from the corners of the four triangular gates, and lying opposite in pairs in two crossed diagonal planes. Inner cortical shell of the same shape, but two-thirds smaller, also thorny. Transverse girdle broad, with four pores on the isthmus. (This species appears to be the common Tetrapyle octacantha, with doubled cortical shell.)

Dimensions.—Length of the first shell 0.04, breadth 0.03; length of the second shell 0.16, breadth 0.12; length of the third shell 0.24, breadth 0.18.

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

5. Tetrapylonium armatum, n. sp.

Outer cortical shell nearly quadrangular, one and a fourth times as long as broad, with very spiny surface. Between numerous smaller (simple or branched) thorns arise twelve larger radial spines, symmetrically distributed, eight wing-spines crossed in two diagonal planes (as in Tetrapylonium octacanthum) and four corner spines on the four rounded corners of the lateral plane (as in Tetrapylonium quadrangulare). Therefore this species combines the armature of both foregoing species. Four gates kidney-shaped. Inner cortical shell elliptical, smooth, three-fourths smaller.

Dimensions.—Length of the first shell 0.045, breadth 0.035; length of the second shell 0.18, breadth 0.15; length of the third shell 0.25, breadth 0.2.

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

Genus 288. Pylozonium,^[23] n. gen.

Definition.—Pylonida with trizonal lentelliptical medullary shell, surrounded by double latticed cortical shell; inner cortical shell as well as the outer Pylonium-shaped, each with three perfect crossed girdles (transverse, lateral, and sagittal).

The genus Pylozonium is the most highly developed form of the Pylonida, as all three systems of concentric girdles here become fully developed, each system with three perfect girdles. In this genus only among all the Pylonida we find nine complete latticed girdles, and in each of the three dimensive planes three concentric elliptical girdles. The first system forms the medullary shell, the second system the inner cortical shell, and the third system the outer cortical shell.

1. Pylozonium novemcinctum, n. sp.

Outer cortical shell lentelliptical, thorny, one and a third times as long as broad, without radial spines, with four kidney-shaped gates. Inner cortical shell of the same shape, but one-third smaller, four times as large as the lentelliptical medullary shell.

Dimensions.—Length of the medullary shell 0.04, breadth 0.03; length of the inner cortical shell 0.16, breadth 0.12; length of the outer cortical shell 0.24, breadth 0.18.

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

2. Pylozonium octacanthum, n. sp. (Pl. 9, fig. 16).

Outer cortical shell lentelliptical, one and a third times as long as broad, with thorny surface and eight long and thin radial spines arising from the corners of the four elliptical gates, and lying opposite in pairs in two crossed diagonal planes. Inner cortical shell of the same shape but one-fourth smaller, about twice as large as the lentelliptical medullary shell.

Dimensions.—Length of the medullary shell 0.065, breadth 0.045; length of the inner cortical shell 0.18, breadth 0.12; length of the outer cortical shell 0.24, breadth 0.18.

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

Family XXVII. Tholonida, n. fam. (Pl. 10).

Definition.—Larcoidea with regular, completely latticed cortical shell, which is composed of two to six or more hemispherical or cap-shaped domes (vaulted chambers or cupolas). The domes lie opposite in pairs on the poles of the three dimensive axes, are separated by annular constrictions, and surround a simple or Larnacilla-shaped central chamber.

The family Tholonida represents a peculiar and very remarkable group of the Larcoidea, distinguished from the other groups of this suborder by the characteristic form of the shell, composed of a variable number of hemispherical domes or cupolas. The middle and original part of the shell is constantly formed of an elliptical or subspherical central chamber, which often, but not constantly, contains a small medullary shell. An even number (two, four, six, or more) of domes is attached to the poles of the three dimensive axes of the central chamber; according as only one, or two, or all three axes develop cupolas, we distinguish in this family three different subfamilies (the Amphitholida, Staurotholida, and Cubotholida). The Amphitholida (or Tholonida monaxonia) form cupolas only on the two poles of one single axis, and this axis corresponds to the minor (or transverse) axis of the central chamber, we find here therefore constantly at least two lateral cupolas (Pl. 10, figs. 1-7). The Staurotholida (or Tholonida diaxonia) form cupolas on the poles of two axes perpendicular one to another; these two axes are the major (principal) and the minor (transverse) axis of the central chamber, we find here therefore constantly at least four cupolas crossed in pairs (Pl. 10, figs. 8-11). The Cubotholida (or Tholonida triaxonia) form cupolas on the poles of all three dimensive axes (perpendicular one to another); corresponding to the principal, transverse, and sagittal axes of the lentelliptical central chamber; therefore we find here constantly at least six cupolas, attached in pairs on the six sides of the central chamber (Pl. 10, figs. 12-17).

The number of genera and species in the family Tholonida is rather large, but the number of individuals is much smaller than in most of the other Spumellaria, and particularly than in the nearly allied Pylonida; the greater number of the species are very rare. Besides this they seem to be very variable and inclined to produce numerous abnormalities. Very often intermediate forms of transition are to be found between the Tholonida and other Larcoidea, particularly the Pylonida and Lithelida. In many species the thick-walled shell is very opaque, and offers great difficulties to the clear study; in the greater number the structure of the shell cannot be understood completely without rolling the shell to the different sides; and the distinction between the Staurotholida and Cubotholida is often very difficult.

The primordial chamber of the Tholonida, or the central chamber in which its growth begins, is either a simple lentelliptical shell (without enclosed medullary shell), like Cenolarcus, or it is a trizonal shell, like Larnacilla, and contains a small concentric medullary shell. But this important inner shell of the central chamber offers peculiar difficulties for study. In many cases (probably in the greater number) there is no doubt the same characteristic trizonal medullary shell, which we found in the Larnacida and Pylonida, and this is our principal argument, if we regard the Tholonida as Larcoidea, which are most nearly allied to both these families, and in which the fenestrated open cortical girdles of the Pylonida are replaced by fenestrated closed cupolas or domes; the characteristic "gates" or large fissures in the cortical shell of the former are therefore here perfectly closed by network. The Tholonida agree in this point with the Larnacida, but are distinguished from them by the prominent vaultings of the hemispherical cupolas or domes, which give them a peculiar appearance. Each pair of domes (opposite on both poles of one dimensive axis) corresponds to one single girdle of the Pylonida.

Regarding the absence or presence of a medullary shell in the central chamber, we may divide the Tholonida into two groups, Cenotholida (without medullary shell) and Coccotholida (with medullary shell). The absence of the medullary shell in many Tholonida may be either primary (original) or secondary (by reduction and loss of it). Probably in the larger proportion (if not always?) its absence is the consequence of reduction and loss, and in this case the Cenotholida must be derived phylogenetically from the Coccotholida, but possibly often (or always?) the contrary may also be the case. At present we cannot find certain arguments for one opinion or the other.

The connection between the medullary (internal) and the cortical (external) shell of the central chamber in the Coccotholida is effected by two lateral wings of a latticed transverse girdle; on both sides of the latter remain the four internal open "gates" of the Pylonida and Larnacida. Very often the limiting edges of these four gates are prolonged into eight external radial spines which lie opposite in pairs in two crossed diagonal planes, and correspond to the eight portal-spines of Tetrapyle octacantha. Besides these, we often find four other beams opposite in pairs in the two crossed axes (principal and lateral). Very often also these radial beams (between medullary and cortical shells) are prolonged on the outside into prominent free radial spines. But other spines may also arise from the surface. Very remarkable is the presence of twenty symmetrically disposed radial spines in some forms of Amphitholida (Amphitholus acanthometra and Amphitholonium acanthonium, &c.). It recalls the twenty radial spines of the Acanthonida, though the laws of distribution in the two similar cases are quite different.

The cortical shell of the Tholonida remains either simple, or it becomes doubled by formation of an outer veil or envelope. This outer cortical shell or "veil" may either repeat completely the typical form of the inner with its cupolas, or it may form an ellipsoidal envelope without dome-shaped partitions. Its network is either like that of the inner, or it is very delicate and irregular, spider-web like. The connection between the two cortical shells is effected by a variable number of radial beams, often prolonged on the outside into radial spines.

The growth of the Tholonida by apposition of new chambers is very characteristic, constantly pairs of chambers originating at both opposite poles of the three dimensive axes, firstly on the transverse axis, secondly on the principal axis, thirdly on the sagittal axis. It is possible that by repeated apposition of new chambers the Tholonida are transformed into Discoidea, but commonly the number of domes is restricted, two in the Amphitholida, four in the Staurotholida, six in the Coccotholida. If new chambers in an irregular manner or in a spiral order be opposed to those first formed pairs of chambers, the Tholonida may be transformed into Soreumida, Streblemida, or Lithelida. The phylogenetic connection between these families is probably very complex and very worthy of further research.

The network of the shell in the Tholonida is sometimes regular, with circular (often hexagonally framed) pores of equal size, sometimes irregular, with roundish pores of unequal size. Commonly the shell is thick and compact; in those genera in which the cortical shell is doubled, the inner is commonly compact, the outer a very delicate veil.

The central capsule of the Tholonida is originally always enclosed by the central chamber, and like this of lentelliptical form, a triaxial ellipsoid. With the apposition of cupolas the growing central capsule may form dome-shaped protuberances which enter into the former. So we may find in the Amphitholida a central capsule with three joints (separated by two annular parallel constrictions), in the Staurotholida a cross-shaped capsule (with four caps around the central lentellipsis), in the Cubotholida a clustered capsule with six caps, surrounding six sides of the cubical central mass. In the Coccotholida (with medullary shell in the central chamber) the latter encloses in the centre the nucleus of the cell. The calymma, or the jelly-veil between the central capsule and the enveloping shell, probably always exhibits annular constrictions, corresponding to those which separate the cupolas of the shell. All these anatomical peculiarities in the Tholonida require a further accurate study.

Synopsis of the Genera of Tholonida.

III. Subfamily Amphitholida. Cupolas developed only in the direction of one single axis (commonly two cupolas). (Tholonida unidimensiva.)	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Central chamber simple, without medullary shell.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Two simple cupolas (without veil),	289. Tholartus.
				Two double cupolas (with veil),	290. Tholodes.
		Central chamber Larnacilla-shaped, with enclosed medullary shell.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Two simple cupolas (without veil),	291. Amphitholus.
				Two double cupolas (with veil),	292. Amphitholonium.
III. Subfamily Staurotholida. Cupolas developed in the direction of two axes perpendicular one to another (commonly four cupolas). (Tholonida bidimensiva.)	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Central chamber simple, without medullary shell.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Four simple cupolas (without veil),	293. Tholostaurus.
				Four double cupolas (with veil),	294. Tholoma.
		Central chamber Larnacilla-shaped, with enclosed medullary shell.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Four simple cupolas (without veil),	295. Staurotholus.
				Four double cupolas (with veil),	296. Staurotholonium.
III. Subfamily Cubotholida. Cupolas developed in the direction of three axes perpendicular one to another (commonly six cupolas). (Tholonida tridimensiva.)	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Central chamber simple, without medullary shell.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Six simple cupolas (without veil),	297. Tholocubus.
				Six double cupolas (with veil),	298. Tholonium.
		Central chamber Larnacilla-shaped, with enclosed medullary shell.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Six simple cupolas (without veil,	299. Cubotholus.
				Six double cupolas (with veil),	300. Cubotholonium.

Subfamily 1. Amphitholida, Haeckel.

Definition.—Tholonida with monaxial growth; cupolas opposite on the poles of one axis. (Shell commonly three-chambered, with two domes on both sides of the central chamber.)

Genus 289. Tholartus,^[24] n. gen.

Definition.—Tholonida with simple cortical shell (without external veil); with two hemispherical cupolas, opposite on the poles of one axis; central chamber between them simple (without medullary shell).

The genus Tholartus (Pl. 10, fig. 1) represents the most simple form of all Tholonida, a three-jointed simple cortical shell without medullary shell; two hemispherical cupolas or domes are attached on both lateral sides of a simple triaxial ellipsoidal central chamber, corresponding to the poles of its lateral or transverse axis. Tholartus may be regarded as the common ancestral form of all Tholonida, and may be derived either from the Pylonida Monozonium (by complete lattice-locking of the lateral wings) or from the Ellipsida Cenellipsis (by development of two lateral protuberances on the poles of the transverse axis). But it is also possible that the absence of the medullary shell is produced by reduction, and in this case Tholartus may be descended from Amphitholus.

Subgenus 1. Tholartella, Haeckel.

Definition.—Surface of the shell smooth or rough, without radial spines.

1. Tholartus tricolus, n. sp. (Pl. 10, fig. 1).

Central chamber one and a half times as high and as broad as both cupolas. Surface of the shell rough. Pores regular, circular, without hexagonal frames, three times as broad as the bars; about sixteen on the half meridian of the central chamber (or its vertical diameter).

Dimensions.—Length of the shell (major axis of the central chamber, vertical) 0.1, breadth of the shell (major axis of the whole three-chambered shell, horizontal) 0.13; pores 0.01, bars 0.003.

Habitat.—Pacific, central area, Station 270, depth 2925 fathoms.

2. Tholartus paniscus, n. sp.

Central chamber of the same breadth, but of the double height of both cupolas. Surface of the shell rough. Pores regular, circular, with hexagonal frames, of the same breadth as the bars; eight to ten on the half meridian of the central chamber.

Dimensions.—Length of the shell (major axis of the central chamber, vertical) 0.12, breadth of the shell (major axis of the whole three-chambered shell, horizontal) 0.15; pores and bars 0.008.

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

3. Tholartus isocolus, n. sp.

Central chamber of the same breadth and height as both cupolas. Surface of the shell smooth. Pores irregular, roundish, once to three times as broad as the bars; ten to fifteen on the half meridian of the central chamber.

Dimensions.—Length of the shell 0.11, breadth 0.14; pores 0.004 to 0.01, bars 0.003.

Habitat.—Pacific, central area, Station 270, depth 2925 fathoms.

Subgenus 2. Tholartissa, Haeckel.

Definition.—Surface of the shell with radial spines.

4. Tholartus tripanis, n. sp.

Central chamber of the same size as both cupolas. Surface of the shell thorny, everywhere covered with short conical radial spines, about as long as the cupolas. Pores regular or subregular, circular, twice as broad as the bars; eight to ten on the half meridian.

Dimensions.—Length of the shell 0.1, breadth 0.12; pores 0.01, bars 0.005.

Habitat.—South Pacific, Station 295, surface.

5. Tholartus sagitta, n. sp.

Central chamber twice as large as both cupolas. Surface of the shell spiny, with eight to twelve regularly (?) distributed radial spines, radiating from the two constrictions between the three chambers. Spines needle-shaped, very thin and long. Pores subregular or irregular, roundish or circular, about three times as broad as the bars; twelve to sixteen on the half meridian.

Dimensions.—Length of the shell 0.11, breadth 0.15; pores 0.01, bars 0.003.

Habitat.—North Pacific, Station 244, surface.

Genus 290. Tholodes,^[25] n. gen.

Definition.—Tholonida with double cortical shell (with external veil), with two hemispherical cupolas, opposite on the poles of one axis; central chamber between them simple (without medullary shell).

The genus Tholodes (Pl. 10, fig. 2) differs from Tholartus, its probable ancestral form, only in the duplication of the shell; the outer shell has exactly the same three-jointed form as the inner; both are connected by eight radial beams, lying in two diagonal planes and corresponding to the eight frontal spines of Tetrapyle octacantha. Possibly Tholodes may also be descended from Amphitholonium by loss of the medullary shell. I have observed only one single specimen of this genus.

1. Tholodes cupula, n. sp. (Pl. 10, fig. 2).

Outer shell of the same form and structure as the inner shell. Central chamber larger than both cupolas. Surface a little rough, without radial spines. Distance of both shells equals the height of the outer cupolas. Pores of both shells regular, circular, three times as broad as the bars; six to seven in the semicircle of one inner cupola, ten to twelve in the semicircle of one outer cupola. Both shells are connected by eight radial beams, crossed in two diagonal planes.

Dimensions.—Major axis of the outer shell 0.1, minor 0.065; major axis of the inner shell 0.05, minor 0.04; pores 0.006, bars 0.002.

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

Genus 291. Amphitholus,^[26] n. gen.

Definition.—Tholonida with simple cortical shell (without external veil), with two hemispherical cupolas, opposite on the poles of one axis; central chamber (between them) Larnacilla-shaped, with medullary shell.

The genus Amphitholus is the most simple form of all Coccotholida (or all Tholonida provided with medullary shell). Its simple cortical shell exhibits, like Tholartus, two lateral hemispheric cupolas, attached on both sides of a lentelliptical central chamber (on the poles of its transverse axis). The central chamber has the form of a triaxial ellipsoid, and contains, like Larnacilla, a small medullary shell, connected with it by the wings of a latticed transverse girdle. Amphitholus may be derived either from Tholartus by secondary production of a cortical shell, or (more probably) from Larnacilla by apposition of two lateral dome-shaped protuberances. In the latter case it may be regarded as an Amphipyle, the lateral open wings of which are closed by lattice-work.

Subgenus 1. Amphitholissa, Haeckel.

Definition.—Surface of the shell smooth or rough, without radial spines.

1. Amphitholus artiscus, n. sp. (Pl. 10, fig. 3).

Central chamber of the same height as both cupolas. Surface of the cortical shell rough. Pores regular, circular, with prominent hexagonal frames, twice as broad as the bars; eight to ten in the basal semicircle of one cupola.

Dimensions.—Major axis of the shell 0.16, minor axis 0.1; pores 0.008, bars 0.004.

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

2. Amphitholus artidium, n. sp.

Central chamber one-fourth higher than both cupolas. Surface of the cortical shell smooth. Pores irregular, roundish, once to three times as broad as the bars. (Very similar to Tholartus tricolus, Pl. 10, fig. 1, but different by the medullary shell.)

Dimensions.—Major axis of the shell 0.15, minor axis 0.12; pores 0.004 to 0.01, bars 0.003.

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

Subgenus 2. Amphitholura, Haeckel.

Definition.—Surface of the shell with radial spines or thorns.

3. Amphitholus octacanthus, n. sp.

Central chamber about twice as high and broad as both cupolas. From the surface arise, symmetrically distributed, eight stout conical radial spines, lying in two diagonal planes, as prolongations of the eight wing-beams, which connect the Tetrapyle-shaped medullary shell with the two ring-like constrictions of the cortical shell. Pores of the latter regular, circular, twice as broad as the bars; ten to twelve in the basal semicircle of one cupola.

Dimensions.—Major axis of the shell 0.15, minor 0.12; pores 0.01, bars 0.005.

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

4. Amphitholus dodecanthus, n. sp.

Central chamber a little larger than both cupolas. From the surface arise twelve strong conical radial spines, four on the poles of the major and the minor axis of the shell, lying in the lateral plane; eight others lying in two diagonal planes, as prolongations of the eight wing-beams, which connect the Tetrapyle-shaped medullary shell with the two ring-like constrictions of the cortical shell. Pores of the latter irregular, roundish, twice to four times as broad as the bars; sixteen to eighteen in the basal semicircle of one cupola.

Dimensions.—Major axis of the shell 0.15, minor 0.11; pores 0.004 to 0.008, bars 0.002.

Habitat.—North Pacific, Station 256, surface.

5. Amphitholus acanthometra, n. sp. (Pl. 10, figs. 5, 6).

Central chamber about twice as broad and as high as both cupolas. On the surface quite symmetrically distributed twenty long and strong cylindrical radial spines; eight in the sagittal plane or in the meridian plane of the central chamber (four opposite in pairs in the principal and the sagittal axes, four others in the middle between the principal and the sagittal spines); four in the horizontal transverse plane, on both sides of the poles of the major or lateral axis; and eight in diagonal planes (corresponding to the eight wing-spines of Tetrapyle octacantha). In the centre of the central chamber is a distinct trizonal medullary shell like that of Tetrapyle, with two vertical columella beams. Pores of the cortical shell subregular, circular, with elevated hexagonal frames, about four times as broad as the bars; five to seven in the semicircle of one cupola. (This remarkable species differs from Tholartus vicenus in the possession of a medullary shell, from Amphitholonium acanthometra by the simple cortical shell. Compare these species).

Dimensions.—Major axis of the shell 0.14 to 0.16, minor axis 0.10 to 0.12; pores 0.015, bars 0.004; major axis of the medullary shell 0.04 to 0.05, minor (horizontal) axis 0.02 to 0.03; length of the twenty radial spines 0.18 to 0.24, basal breadth 0.01.

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

6. Amphitholus armatus, n. sp.

Central chamber twice as broad, but of the same height, as the flat vaulted cupolas. Surface armed with thirty to forty very large three-sided prismatic spines, longer than the major axis of the shell. Pores irregular, roundish, twice to five times as broad as the bars; eight to nine on the basal semicircle of one cupola.

Dimensions.—Major axis of the shell 0.15, minor axis 0.1; pores 0.006 to 0.015, bars 0.003; length of the spines 0.2 to 0.25, breadth 0.01.

Habitat.—North Atlantic, Station 353, surface.

7. Amphitholus polyacanthus, n. sp.

Central chamber of the same breadth and height as both cupolas. Surface armed with very numerous (sixty to eighty) strong conical spines, about as long as the minor axis of the shell. Pores subregular, circular, twice as broad as the bars; sixteen to eighteen in the basal semicircle of one cupola.

Dimensions.—Major axis of the shell 0.13, minor 0.08; pores 0.006, bars 0.003; length of the radial spines 0.09, breadth 0.006.

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

8. Amphitholus panicium, n. sp. (Pl. 10, fig. 4).

Central chamber ellipsoidal, nearly twice as broad, but of the same height, as both cupolas. Whole surface thorny; the largest radial thorns about as long as the medullary shell. Pores irregular, roundish, twice to four times as broad as the bars. On the base of each cupola a circle of ten to twelve larger square pores, separated by radial beams, which are prolonged into stouter free spines. This remarkable formation of the cupolas, very rare in this family, recalls the characteristic formation of the distal chambers of the Panartida and Zygartida (e.g., Pl. 40, figs. 4, 8, &c.), where it is very common.

Dimensions.—Major axis of the shell 0.15, minor 0.1; pores 0.005 to 0.012, bars 0.003; large square pores 0.02; axes of the medullary shell 0.03 and 0.02.

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

Genus 292. Amphitholonium,^[27] n. gen.

Definition.—Tholonida with double cortical shell (with external veil), with two hemispherical cupolas, opposite on the poles of one axis; central chamber (between them) Larnacilla-shaped, with medullary shell.

The genus Amphitholonium differs from the nearly allied Amphitholus (probably its ancestral form) only in the duplication of the cortical shell; the outer has the same three-jointed form as the inner, and is connected with it by a variable number of radial beams. From the similar Tholodes it differs in the possession of a medullary shell.

1. Amphitholonium tricolonium, n. sp. (Pl. 10, fig. 7).

Outer cortical shell smooth, of the same three-jointed form as the inner, at an equal distance from it throughout the whole circumference; central chamber higher-vaulted than both cupolas. Network of the outer shell delicate, with subregular, circular pores. Pores of the thick-walled inner shell subregular, circular, with hexagonal frames, three times as broad as the bars; eight to ten in the basal semicircle of one cupola.

Dimensions.—Major axis of the outer cortical shell 0.2, minor axis 0.15; major axis of the inner cortical shell 0.16, minor axis 0.11; pores 0.01, bars 0.0035.

Habitat.—South Pacific, Station 302, depth 1450 fathoms.

2. Amphitholonium octostylium, n. sp.

Outer cortical shell lentelliptical, smooth, not articulated, at a varying distance from the three-jointed inner shell; central chamber of the latter twice as high as both hemispherical cupolas. Network of the outer shell very thin, cob-web like. Pores of the inner shell subregular, roundish, twice as broad as the bars; six to seven in the semicircle of one cupola. Eight thin and long, bristle-shaped, radial spines, opposite in pairs in two crossed diagonal planes.

Dimensions.—Major axis of the outer cortical shell 0.16, minor 0.12; major axis of the inner cortical shell 0.12, minor 0.09; pores 0.01, bars 0.005.

Habitat.—Pacific, central area, Station 273, depth 2350 fathoms.

3. Amphitholonium acanthonium, n. sp.

Outer cortical shell of the same three-jointed form as the inner, at a uniform distance from it; central chamber higher vaulted than both cupolas. Network of the outer shell irregular, delicate, of the inner regular, strong, with circular, hexagonally framed pores, three times as broad as the bars; eight to nine in the semicircle of one cupola. On the surface, quite symmetrically disposed, twenty long and strong, cylindrical, radial spines; eight in the sagittal plane, four in the transverse plane; eight in two diagonal planes between the former and the latter. The remarkable geometric disposition of the twenty spines is in this species quite the same as in Amphitholus acanthometra. It differs from this nearly allied species in the double cortical shell.

Dimensions.—Major axis of the outer cortical shell 0.18, minor 0.14; major axis of the inner cortical shell 0.14, minor 0.1; pores 0.012, bars 0.004.

Habitat.—South Pacific, Station 295, surface.

Subfamily 2. Staurotholida, Haeckel.

Definition.—Tholonida with diaxial growth; cupolas crossed in pairs, opposite on the poles of two axes, perpendicular one to another. (Shell commonly five-chambered, with four domes, cross-wise surrounding the central chamber.)

Genus 293. Tholostaurus,^[28] n. gen.

Definition.—Tholonida with simple cortical shell (without external veil), composed of four hemispherical cupolas in cross-form, opposite in pairs on the poles of two axes perpendicular one to another; central chamber simple (without medullary shell).

The genus Tholostaurus is the most simple form of the Staurotholida, or the Tholonida with four crossed hemispherical cupolas, lying on the poles of two axes perpendicular one to another. The central chamber communicates by four wide openings with the four domes, and contains no medullary shell. Tholostaurus may originate either from Tholartus by apposition of two opposite cupolas between the first pair, or from Staurotholus by loss of the medullary shell.

Subgenus 1. Tholostaurantha, Haeckel.

Definition.—Surface of the shell smooth or rough, without radial spines.

1. Tholostaurus quadrigatus, n. sp.

All four cupolas nearly of the same size and form, subregular. Surface smooth, without radial spines. Pores subregular, circular, four times as broad as the bars; eight to ten pores in the basal semicircle of one cupola.

Dimensions.—Diameter of the shell 0.12; pores 0.008, bars 0.002.

Habitat.—Pacific, central area, Station 272, surface.

2. Tholostaurus cruciformis, n. sp.

Two opposite cupolas larger than the two others. Surface rough, without radial spines. Pores regular, circular, hexagonally framed, twice as broad as the bars; twelve to fourteen in the basal semicircle of one cupola.

Dimensions.—Major axis of the shell 0.16, minor axis 0.12; pores 0.006, bars 0.003.

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

Subgenus 2. Tholostauroma, Haeckel.

Definition.—Surface of the shell with radial spines or thorns.

3. Tholostaurus tetrabelonis, n. sp.

All four cupolas nearly of the same size and form, subregular. Pores regular, circular, hexagonally framed, twice as broad as the bars; twelve to fourteen in the semicircle of one cupola. Four long and stout conical radial spines, two vertical on the poles of the principal axis, two horizontal on the poles of the transverse axis.

Dimensions.—Major axis of the shell 0.15, minor 0.13; pores 0.006, bars 0.003.

Habitat.—South Pacific, Station 288, surface.

4. Tholostaurus octobelonis, n. sp.

Two opposite cupolas larger than the two others. Pores subregular, circular, three times as broad as the bars; ten to twelve in the semicircle of one cupola. Eight long and thin, needle-shaped, radial spines, in pairs crossed in two diagonal planes.

Dimensions.—Major axis of the shell 0.16, minor 0.12; pores 0.01, bars 0.003.

Habitat.—South Pacific, Station 291, surface.

5. Tholostaurus dodecabelos, n. sp.

Two opposite cupolas larger than the two others. Pores irregular, roundish, twice to three times as broad as the bars; six to eight in the semicircle of one cupola. Twelve thin and long radial spines, four on the poles of the two crossed axes (principal and lateral), eight crossed in two diagonal planes.

Dimensions.—Major axis of the shell 0.14, minor 0.11; pores 0.006 to 0.01, bars 0.003.

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

6. Tholostaurus polybelonis, n. sp.

Two opposite cupolas larger than the two others. Pores circular, hexagonally framed, of the same breadth as the bars; ten to twelve in the semicircle of one cupola. Numerous (twenty to thirty or more) thin, bristle-like, radial spines, about as long as the radius of the shell.

Dimensions.—Major axis of the shell 0.15, minor axis 0.12; pores and bars 0.007.

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

Genus 294. Tholoma,^[29] n. gen.

Definition.—Tholonida with double cortical shell (with external veil), composed of four hemispherical cupolas in cross-form, opposite in pairs on the poles of two axes perpendicular one to another; central chamber simple (without medullary shell).

The genus Tholoma (Pl. 10, figs. 10, 13) differs from the preceding Tholostaurus (its probable ancestral form) only in the duplication of the shell. The outer (secondary) shell has the same cross-form as the inner (primary) shell. In the two observed species the growth seems to be different, in the first species all four cupolas of each cross being of the same size, form, and age; in the second two opposite cupolas, larger and apparently older than the other two. Tholoma is possibly the offspring of Staurotholonium, from which it may have been produced by loss of the medullary shell.

Subgenus 1. Tholomantha, Haeckel.

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

1. Tholoma quadrigeminum, n. sp. (Pl. 10, fig. 10).

All four chambers in each cortical shell nearly equal, subregular. Surface smooth, without radial spines. Structure of the network in both shells similar. Pores regular, circular, twice as broad as the bars; six to eight in the basal semicircle of one inner, ten to twelve in the semicircle of one outer cupola.

Dimensions.—Diameter of the outer shell 0.14, of the inner 0.09; pores 0.006, bars 0.003.

Habitat.—South Pacific, Station 302, surface.

Subgenus 2. Tholomura, Haeckel.

Definition.—Surface of the shell with radial spines.

2. Tholoma metallasson,^[30] n. sp. (Pl. 10, fig. 13).

Two opposite chambers in each cortical shell larger than the two others; the larger chambers of the inner shell corresponding to the smaller chambers of the outer shell. Network in both shells of the same structure, regular, with circular, hexagonally framed pores of the same breadth as the bars; eight to ten in the semicircle of an inner, fourteen to sixteen in the semicircle of an outer cupola. Numerous (twenty to thirty or more) thin, cylindrical, bristle-shaped, long radial spines, symmetrically disposed.

Dimensions.—Major axis of the outer shell 0.26, minor axis 0.2; major axis of the inner shell 0.16, minor axis 0.13; pores and bars 0.006.

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

Genus 295. Staurotholus,^[31] n. gen.

Definition.—Tholonida with simple cortical shell (without external veil), composed of four hemispherical cupolas in cross-form, opposite in pairs on the poles of two axes perpendicular one to another; central chamber Larnacilla-shaped (with enclosed medullary shell).

The genus Staurotholus differs from Tholostaurus in the possession of a medullary shell in the central chamber, and may be derived from this genus by its production. But it may also be derived from Amphitholus by apposition of two secondary opposite cupolas between the two primary cupolas. The symmetrical position of an increasing number of radial spines in the different species is remarkable (resembling Tholostaurus as well as Amphitholus).

Subgenus 1. Staurotholissa, Haeckel.

Definition.—Surface of the shell smooth or rough, without radial spines.

1. Staurotholus quadratus, n. sp.

Surface of the cortical shell smooth. All four cupolas nearly of the same size and form; therefore principal and lateral axes equal. Pores regular, circular, with hexagonal frames, twice as broad as the bars; eight to ten on the basal semicircle of one cupola. Medullary shell square.

Dimensions.—Diameter of the cortical shell 0.15; pores 0.01, bars 0.005.

Habitat.—South Atlantic, Station 323, depth 1900 fathoms.

2. Staurotholus cruciatus, n. sp.

Surface of the cortical shell rough. The two principal cupolas somewhat larger than the two lateral cupolas; therefore the longitudinal axis longer than the transverse. Pores irregular, roundish, twice to three times as broad as the bars; twelve to sixteen in the semicircle of one cupola.

Dimensions.—Major axis of the shell 0.16, minor 0.13; pores 0.005 to 0.009, bars 0.003.

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

Subgenus 2. Staurotholura, Haeckel.

Definition.—Surface of the shell with radial spines.

3. Staurotholus tetrastylus, n. sp. (Pl. 10, fig. 8).

The two principal cupolas smaller than the two lateral cupolas. Pores subregular, circular, three times as broad as the bars; six to eight in the semicircle of one cupola. Medullary shell elliptical. On the surface four long cylindrical radial spines; two in the principal and two in the lateral axis.

Dimensions.—Major axis of the cortical shell 0.15, minor 0.12; pores 0.012, bars 0.004.

Habitat.—South Pacific, Station 166, surface.

4. Staurotholus octostylus, n. sp.

The two lateral cupolas larger than the two principal cupolas. Pores subregular, circular, twice as broad as the bars; ten to twelve in the semicircle of one cupola. Medullary shell hexagonal, connected with each ring-like constriction by eight strong cylindrical radial spines (longer than the whole shell), lying in two crossed meridian planes, and corresponding to the eight diagonal wing-spines of Tetrapyle octacantha.

Dimensions.—Major axis of the cortical shell 0.12, minor 0.1; pores 0.008, bars 0.004.

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

5. Staurotholus decastylus, n. sp.

The two principal cupolas twice as broad and high as the two lateral cupolas. Pores subregular, circular, four times as broad as the bars; six to eight in the semicircle of one cupola. Ten long and thin radial spines with thickened conical bases, about as long as the major axis of the shell, by inner prolongations connected with the lentelliptical medullary shell; two polar spines in the principal axis, eight wing-spines in two crossed diagonal planes.

Dimensions.—Major axis 0.12, minor 0.1; pores 0.012, bars 0.003.

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

6. Staurotholus dodecastylus, n. sp. (Pl. 10, fig. 9).

The two lateral cupolas larger than the two principal cupolas. Pores subregular, circular, three times as broad as the bars; five to seven in the semicircle of one cupola. Twelve strong cylindrical radial spines, four on the poles of the two larger axes (two principal and two lateral), eight wing-spines in two crossed diagonal planes. Medullary shell hexagonal.

Dimensions.—Major (lateral) axis 0.11, minor (principal) 0.09; pores 0.009, bars 0.003.

Habitat.—Tropical Atlantic, Station 348, surface.

7. Staurotholus polystylus, n. sp.

The two principal cupolas larger than the two lateral cupolas. Pores irregular, roundish, twice to three times as broad as the bars; ten to twelve in the semicircle of one cupola. On the surface numerous thin bristle-shaped spines (twenty to thirty or more).

Dimensions.—Major axis 0.14, minor 0.11; pores 0.006 to 0.01, bars 0.003.

Habitat.—North Pacific, Station 231, surface.

Genus 296. Staurotholonium,^[32] n. gen.

Definition.—Tholonida with double cortical shell (with external veil), composed of four hemispherical cupolas in cross-form, opposite in pairs on the poles of two axes perpendicular one to another; central chamber Larnacilla-shaped (with medullary shell).

The genus Staurotholonium differs from the nearly allied Staurotholus (its probable ancestral form) only in the duplication of the cortical shell. The outer shell commonly repeats the cross-form of the inner, with four corresponding cupolas; but sometimes the four cupolas of the outer shell alternate in size and form with those of the inner, or the outer shell forms a simple lenticular envelope around the inner. From the similar Tholoma, Staurotholonium differs in the possession of a medullary shell in the central chamber.

Subgenus 1. Staurotholodes, Haeckel.

Definition.—Surface of the outer cortical shell smooth or rough, without radial spines.

1. Staurotholonium biquadratum, n. sp.

Outer cortical shell smooth, of the same regular crucial form as the inner, equidistant from it everywhere. Form and structure of both cortical shells nearly the same, but the outer about twice as large as the inner; both connected only by eight diagonal beams. All four cupolas of each cortical shell regular, of the same size. Pores regular, circular, twice as broad as the bars; six to eight in the basal semicircle of each cupola. Medullary shell square. (Similar to Staurotholus quadratus, but differs by the double cortical shell.)

Dimensions.—Diameter of the outer cortical shell 0.16, of the inner 0.08, of the medullary shell 0.04; pores of the inner cortical shell 0.006, bars 0.003.

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

2. Staurotholonium bicruciatum, n. sp.

Outer cortical shell rough, twice as large as the inner, of the same form and structure, at an equal distance from it. In both shells the principal cupolas are larger than the lateral. Pores irregular, roundish, in the outer shell four times, in the inner twice as large as the bars; eight to ten in the basal semicircle of one cupola. (Similar to Staurotholus cruciatus, but differs mainly in the double cortical shell.) Medullary shell lentelliptical.

Dimensions.—Major (longitudinal) axis of the outer cortical shell 0.016, of the inner 0.08; minor (transverse) axis of the former 0.14, of the latter 0.07; medullary shell 0.03 to 0.04.

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

3. Staurotholonium alternatum, n. sp.

Outer cortical shell smooth, very different from the inner; in the outer the two principal cupolas are larger than the two lateral; in the inner inversely smaller. Pores subregular, circular, in the outer shell four times, in the inner shell twice as broad as the bars; ten to twelve pores in the basal semicircle of one cupola.

Dimensions.—Major axis (length) of the outer cortical shell 0.15, minor (breadth) 0.13; pores 0.012, bars 0.003; major axis (length) of the inner cortical shell 0.11, minor axis (breadth) 0.09; pores 0.006, bars 0.003.

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

4. Staurotholonium lenticulare, n. sp.

Outer cortical shell smooth, lenticular, with circular circumference, with very delicate irregular network and small roundish pores. Its distance from the inner much greater in the four diagonal points than in the four polar points. Inner cortical shell regular, cross-like, with four cupolas of similar size and form. Pores subregular, circular, twice as broad as the bars; eight to ten in the basal semicircle of one cupola. Medullary shell lenticular.

Dimensions.—Diameter of the outer cortical shell 0.16, of the inner 0.12; pores of the inner 0.008, bars 0.004.

Habitat.—North Atlantic, Station 353, surface.

Subgenus 2. Staurotholoma, Haeckel.

Definition.—Surface of the outer cortical shell with radial spines or thorns.

5. Staurotholonium octodoratium, n. sp.

Outer cortical shell of the same form and structure as the inner, but twice as large, both principal domes somewhat larger than both lateral. Pores subregular, circular, of the same breadth as the bars; five to six in the semicircle of one inner, eight to ten of one outer cupola. Eight thin and long bristle-like spines, opposite in pairs in two crossed diagonal planes.

Dimensions.—Major axis of the outer cortical shell 0.15, minor 0.12; major axis of the inner cortical shell 0.07, minor 0.06; pores and bars 0.005.

Habitat.—North Pacific, Station 231, surface.

6. Staurotholonium octodoronium, n. sp. (Pl. 10, fig. 11).

Outer cortical shell of the same form as the inner, both little distant; network of the outer irregular and delicate. Pores of the inner regular, circular, twice as broad as the bars; seven to nine in the basal semicircle of one cupola. Both lateral domes larger than the principal. Eight long and thin, cylindrical radial spines opposite in pairs in two crossed diagonal planes.

Dimensions.—Major axis of the outer cortical shell 0.2, minor 0.18; major axis of the inner cortical shell 0.16, minor 0.14; pores 0.008, bars 0.004.

Habitat.—South Pacific, Station 288, surface.

Subfamily 3. Cubotholida, Haeckel.

Definition.—Tholonida with triaxial growth; cupolas lying in pairs on the six sides of a cubical central chamber, opposite at the poles of three axes perpendicular one to another. (Shell commonly seven-chambered, with six domes surrounding the central chamber.)

Genus 297. Tholocubus,^[33] n. gen.

Definition.—Tholonida with simple cortical shell (without external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the simple cuboidal central chamber (without medullary shell).

The genus Tholocubus is the most simple form of the Cubotholida, or of the Tholonida with domes situated in three axes perpendicular one to another; six hemispherical cupolas lying on the six sides of a cuboidal central chamber; this latter contains no medullary shell. Tholocubus may be derived phylogenetically either from Tholostaurus by apposition of two opposite domes on the flat sides of the cross-shell, or from Cubotholus by loss of the medullary shell.

Subgenus 1. Tholocubulus, Haeckel.

Definition.—Surface of the shell smooth or rough, without radial spines.

1. Tholocubus tessellatus, n. sp. (Pl. 10, fig. 12).

Surface of the shell smooth, without radial spines. Pores regular, circular, hexagonally framed, twice as broad as the bars; eight to twelve pores on the semicircle of one cupola. Principal cupolas smaller than the lateral, larger than the sagittal cupolas.

Dimensions.—Diameter of the shell 0.15; pores 0.01, bars 0.005.

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

2. Tholocubus tesserarius, n. sp.

Surface of the shell rough, without radial spines. Pores irregular, roundish, once to three times as broad as the bars; twelve to sixteen pores in the semicircle of one cupola. All six cupolas nearly of the same size.

Dimensions.—Diameter of the shell 0.16; pores 0.004 to 0.008, bars 0.003.

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

Subgenus 2. Tholocubitus, Haeckel.

Definition.—Surface of the shell with radial spines or thorns.

3. Tholocubus tesseralis, n. sp. (Pl. 10, fig. 16).

Surface of the shell with numerous (eight to sixteen) thin and long, bristle-shaped radial spines (the greater part broken off in the figured specimen); pores subregular, circular, three to four times as broad as the bars; ten to twelve in the semicircle of one cupola.

Dimensions.—Major axis of the shell 0.16, minor axis 0.14; pores 0.01, bars 0.0027.

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

Genus 298. Tholonium,^[34] n. gen.

Definition.—Tholonida with double cortical shell (with external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the simple cuboidal central chamber (without medullary shell).

The genus Tholonium (Pl. 10, fig. 17) differs from the preceding Tholocubus only in the duplication of the cortical shell. The outer (secondary) shell forms either a simple (spheroidal or ellipsoidal) thin veil around the inner (primary) shell, or both shells are of the same form, with six corresponding cupolas. Possibly Tholonium is the offspring of Cubotholonium, having originated by loss of the medullary shell.

Subgenus 1. Tholonetta, Haeckel.

Definition.—Surface of the shell smooth or rough, without radial spines or thorns.

1. Tholonium bicubicum, n. sp.

Outer shell with six hemispherical dome-shaped protuberances, corresponding in those of the inner shell. Both shells connected by numerous radial beams. Surface of the outer shell smooth; its network nearly of the same shape as that of the inner, with subregular, circular pores, twice as broad as the bars; ten to fifteen pores on the semicircle of one cupola.

Dimensions.—Diameter of the outer shell 0.14, of the inner 0.12; pores of the latter 0.006, bars 0.003.

Habitat.—South Atlantic, Station 325, depth 2650 fathoms.

2. Tholonium ellipticum, n. sp.

Outer shell ellipsoidal, without dome-shaped protuberances, with smooth surface, without radial spines; network delicate, with subregular, circular pores. Inner shell with regular, circular, hexagonally framed pores, twice as broad as the bars; ten to twelve pores on the semicircle of one cupola.

Dimensions.—Major axis of the outer shell 0.16, minor axis 0.14; major axis of the inner shell 0.14, minor axis 0.12; pores 0.008, bars 0.004.

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

3. Tholonium sphæricum, n. sp.

Outer shell spherical, without dome-shaped protuberances, with smooth surface, without radial spines; network very delicate, with very small subregular, circular pores. Inner shell with regular, circular pores of the same breadth as the bars; fourteen to sixteen on the basal semicircle of one cupola.

Dimensions.—Diameter of the spherical outer shell 0.15, inner shell 0.12; pores and bars of the inner shell 0.005.

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

Subgenus 2. Tholonilla, Haeckel.

Definition.—Surface of the outer shell covered with radial spines or thorns.

4. Tholonium hexonium, n. sp. (Pl. 10, fig. 17).

Outer shell ellipsoidal, without dome-shaped protuberances, covered with numerous (thirty to fifty) thin and long, bristle-shaped radial spines; network very delicate, irregular, with roundish pores. Inner shell with six marked hemispherical domes of somewhat different sizes; pores regular, circular, with prominent hexagonal frames, twice as broad as the bars; ten to twelve on the basal semicircle of one cupola.

Dimensions.—Major axis of the outer shell 0.15, minor axis 0.14; major axis of the inner shell 0.13, minor axis 0.12; pores 0.008, bars 0.004.

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

5. Tholonium sphæronium, n. sp.

Outer shell very thin walled, spherical, without dome-shaped protuberances, with smooth surface, excepting eight large radial spines, rising from the eight corners of the inner cubical central chamber. Pores of the outer shell very small, subcircular. Inner shell very thick walled, with six marked hemispherical domes; pores subregular, circular, with prominent hexagonal frames, twice as broad as the bars; six to eight on the semicircle of one cupola.

Dimensions.—Diameter of the spherical outer shell 0.15, inner shell 0.11; pores of the inner 0.01, bars 0.005.

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

Genus 299. Cubotholus,^[35] n. gen.

Definition.—Tholonida with simple cortical shell (without external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the cuboidal Larnacilla-shaped central chamber (with medullary shell).

The genus Cubotholus differs from Tholocubus in the possession of a medullary shell in the central chamber, and may be derived from this genus by its production; but it may also be derived from Staurotholus by apposition of two opposite domes on the flat sides of the cross-shell. Sometimes all six domes are of the same size and form, but commonly different in pairs.

Subgenus 1. Cubotholissa, Haeckel.

Definition.—Surface of the shell smooth or rough, without radial spines.

1. Cubotholus regularis, n. sp. (Pl. 10, fig. 14).

On the six sides of the cubical central chamber six hemispherical cupolas of the same size and form. Surface smooth. Pores regular, circular, twice as broad as the bars; eight in the basal semicircle of each cupola. Medullary shell apparently spherical (?), connected with the eight corners of the central chamber by eight radial beams, regularly disposed. (This species is remarkable for the perfect symmetry of the shell, the six sides of which appear to be quite similar. It differs from the similar Tholocubus regularis in the possession of a medullary shell.)

Dimensions.—Diameter of the cortical shell (equal in all three dimensive axes) 0.15; pores 0.01, bars 0.005; diameter of the medullary shell 0.04.

Habitat.—Pacific, central area, Station 273, depth 2350 fathoms.

2. Cubotholus quadraticus, n. sp.

Surface of the shell smooth. Both principal cupolas (on the poles of the longitudinal axis) larger than the four other cupolas, which have the same size and lie cross-wise in the equatorial plane. (Therefore two of the three fundamental axes equal, the third larger.) Pores subregular, circular, three times as broad as the bars; ten to twelve in the semicircle of each cupola-basis.

Dimensions.—Major axis 0.16, minor axis 0.12; pores 0.012, bars 0.004.

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

3. Cubotholus rhombicus, n. sp.

Surface of the shell smooth. Both principal cupolas (on the poles of the longitudinal axis) larger than the two lateral (on the poles of the transverse axis), and these larger than the two sagittal cupolas (on the poles of the sagittal axis). Therefore all three fundamental axes unequal. Pores irregular, roundish, twice to four times as broad as the bars; eight to twelve in the basal semicircle of each cupola. Medullary shell lentelliptical.

Dimensions.—Major (principal) axis 0.16, middle (lateral) axis 0.14, minor (sagittal) axis 0.12; pores 0.006 to 0.012, bars 0.003.

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

Subgenus 2. Cubotholura, Haeckel.

Definition.—Surface of the shell with radial spines or thorns.

4. Cubotholus octoceras, n. sp.

All six cupolas in pairs of different sizes. Both principal domes larger than the lateral domes, and these larger than the sagittal domes. Pores subregular, circular, twice as broad as the bars; eight to ten in the semicircle of each cupola. From the surface arise (at the intersecting points of every three cupolas) eight strong conical radial spines, about as long as the shell-axis; they lie in two diagonal planes, and are the external free prolongations of eight inner beams (homologous with the eight wing-spines of Tetrapyle octacantha), which connect the lentelliptical medullary shell with the eight corners of the cuboidal central chamber.

Dimensions.—Major axis of the cortical shell 0.15, middle 0.13, minor 0.11; pores 0.008, bars 0.004; diameters of the medullary shell corresponding to 0.05, 0.04, 0.03.

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

Genus 300. Cubotholonium,^[36] n. gen.

Definition.—Tholonida with double (or sometimes triple) cortical shell (with external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the cuboidal Larnacilla-shaped central chamber (with medullary shell).

The genus Cubotholonium differs from the nearly allied Cubotholus (its probable ancestral form) only in duplication of the cortical shell. I have observed only two species of this rare form, both rather different. In the first species the outer cortical shell forms a simple spherical thin veil around the inner, the six cupolas of which are nearly of the same form and size. In the second species each of the domes of the inner cortical shell is protected by an outer larger cupola, and besides this the whole shell is enveloped by a thin ellipsoidal veil (Pl. 10, fig. 15). Therefore this species may be the representative of a peculiar genus, the most highly developed of all Tholonida—Tholothauma.

1. Cubotholonium sphæroides, n. sp.

Outer cortical shell (or veil) spherical, with smooth surface; network very delicate, with very thin bars and very small irregular, roundish pores. Inner cortical shell simple, composed of six hemispherical cupolas, surrounding the six sides of the cubical central chamber, which encloses a spherical medullary shell (one-third as large as itself). Network of the inner cortical shell regular, with circular pores of the same breadth as the bars, twelve to fourteen in the basal semicircle of one cupola.

Dimensions.—Diameter of the spherical outer shell 0.2, of the inner cortical shell 0.15; pores and bars of the latter 0.006.

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

2. Cubotholonium ellipsoides, n. sp. (Pl. 10, fig. 15).

Tholothauma ellipsoides, Haeckel, 1883, MS.

Outer cortical shell (or veil) ellipsoidal, with very thin irregular network and thorny surface. Inner cortical shell double, with six double, flatly vaulted cupolas, surrounding the six sides of the Larnacilla-shaped central chamber; the double domes of each shell are in opposite pairs somewhat larger than the alternating pairs. Pores subregular, circular, about the same breadth as the bars; eight to twelve in the basal semicircle of one cupola. Central chamber with ellipsoidal medullary shell. Radial spines short, very numerous.

Dimensions.—Major axis of the outer cortical shell 0.28, minor 0.24; major axis of the inner cortical shell 0.16, minor axis 0.14; pores and bars 0.006; medullary shell 0.03.

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

Family XXVIII. Zonarida, n. fam. (Pl. 50, figs. 9-12).

Definition.—Larcoidea with regular, completely latticed cortical shell, distinguished by two to four or more annular constrictions, which lie (all or partly) in the dimensive planes (sagittal, transverse, or lateral), and by which four to eight or more vaulted cupolas or dome-like chambers become separated. In the centre of this chambered cortical shell lies constantly a trizonal or Larnacilla-shaped medullary shell.

The family Zonarida comprises a small number of peculiar Larcoidea, resembling the Tholonida in the composition of the polythalamous cortical shell by a number of cupolas or dome-shaped protuberances. But the disposition and origin of these latter are quite different. Whilst in the Tholonida the axes of the domes are dimensive axes, and these are separated by annular constrictions lying in diagonal planes, in the Zonarida we find the contrary; the axes of the domes are here diagonal axes, and these are separated by annular constrictions lying in dimensive planes. However, this definition agrees absolutely only in the four-chambered Zonarium and in the eight-chambered Zonidium, whilst in the six chambered Zoniscus only four domes are disposed according to this law, two others, however, in the same manner as in the Tholonida. Therefore this genus is intermediate between both families.

The Cortical Shell of the Zonarida is in all cases completely latticed and of regular lentelliptical fundamental form, as in the nearly allied Larnacida and Tholonida. The three dimensive axes are constantly of different sizes, each with two equal poles; commonly (as in the human body) the principal or longitudinal axis is the longest, the sagittal (or dorso-ventral) axis the shortest; the transverse (or lateral) axis being intermediate between them. Of the three dimensive planes the lateral plane is the largest (determined by the principal and transverse axes); the smallest is the equatorial plane (crossed by the transverse and sagittal axes); the sagittal plane (determined by the sagittal and principal axes) being intermediate between them.

The annular constrictions of the cortical shell which produce the dome-shaped protuberances are different in number in the three known genera—two, three, or four. To each constriction often (but not always) corresponds an internal latticed septum, which connects the cortical with the medullary shell. The number of the cupolas is always double the number of the annular constrictions by which they are separated, therefore four, six, or eight.

In all known Zonarida the sagittal septum is quite constant, but derived from the original axial rod, which lies in the principal axis. By ramification of this axial beam and reticular connection with the sagittal girdle arises the sagittal septum, which we found first in Octopyle, halving the four gates of Tetrapyle. Whilst this sagittal septum (between right and left halves of the body) is common to all three known genera of this family, the number and shape of the other annular constrictions are different. In Zonarium (Pl. 50, fig. 9) we find only one transverse constriction (in the equatorial plane), in Zoniscus (figs. 10, 11) two parallel transverse constrictions (parallel to the equatorial plane, on both sides of it). Zonidium (fig. 12) is a combination of both foregoing genera; it has three parallel transverse constrictions (one in the equatorial plane, and one on each side of it).

The Latticed Domes (cupolas or chambers) of the cortical shell exhibit correspondingly a different number and disposition in the three known genera. In Zonarium are found only four crossed chambers, separated by the sagittal and transverse septa; the axes of the four crossed domes are diagonal axes, whilst in the similar Staurotholus they are dimensive axes (principal and transverse axes). In Zonidium we find eight domes, each cupola of Zonarium being halved by a diagonal septum. Zoniscus is intermediate between the two foregoing genera, and has six cupolas, three on each side of the sagittal septum.

The inner communication of the cupolas or chambers is more or less free, the lattice-work of the separating septa between them commonly remaining more or less imperfect, or represented only by some isolated beams or meshes. The outer network of the cupolas is commonly irregular (as in the majority of Larcoidea), but sometimes distinguished by a small number of regularly disposed larger apertures (similar to the "gates" of the Pylonida). From the surface radial spines often arise in characteristic number and symmetrical disposition, commonly as prolongations of the septal axes or of the constricted edges.

The Medullary Shell in all Zonarida is a true trizonal or Larnacilla-shaped lattice-shell (compare above, p. 600); its perimeter (or the first lateral girdle) is sometimes more elliptical, at other times more hexagonal; the hexagon is amphithect; both its lateral sides are often concave and commonly longer than the four other sides.

The Central Capsule in all Zonarida is in a strict geometrical sense a true lentellipsis (compare above, p. 599); its principal axis is commonly one and a third to one and a half times as great as the transverse axis, and twice to three times as great as the sagittal axis. The lentelliptical central capsule encloses the trizonal medullary shell, whilst it is externally enveloped by the chambered cortical shell.

Synopsis of the Genera of Zonarida.

Two annular constrictions and four cupolas,	301. Zonarium.
Three annular constrictions and six cupolas,	302. Zoniscus.
Four annular constrictions and eight cupolas,	303. Zonidium.

Genus 301. Zonarium,^[37] n. gen.

Definition.—Zonarida with four dome-shaped chambers of the cortical shell, separated by two annular constrictions (one sagittal and one transverse).

The genus Zonarium is the most simple form of the Zonarida, and differs from the nearly allied Larnacalpis by two ring-like constrictions, which are crossed at right angles, one in the sagittal (or median) plane, and one in the transverse (or equatorial) plane. By these two annular constrictions four egg-shaped or kidney-shaped chambers become imperfectly separated, which correspond to the quadrants of the lateral plane. The first cause of the marked constrictions may be the formation of the latticed sagittal septum, which is found first in Octopyle, as halving the four gates of Tetrapyle. Between this septum and the constricted narrow transverse girdle the cortical shell grows out in the form of four vaulted cupolas; every two opposite domes are congruent, two neighbouring are symmetrically equal.

1. Zonarium quadrigatum, n. sp.

Cortical shell quadrangular, one and a half times as long as broad, with four rounded corners. Surface thorny, with numerous short radial spines. Sagittal constriction twice as long as the hexagonal medullary shell. Four cupolas kidney-shaped.

Dimensions.—Length of the cortical shell 0.16, breadth 0.11; length of the medullary shell 0.06, breadth 0.04.

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

2. Zonarium quadrispinum, n. sp.

Cortical shell quadrangular, nearly rectangular, about twice as long as broad, with four corners, from which arise four strong, three-sided pyramidal, radial spines (crossed in two diagonals of the lateral plane). Surface thorny, only smooth in the transverse constriction. Sagittal constriction three times as long as the lentelliptical medullary shell. Four cupolas elliptical or nearly quadrangular.

Dimensions.—Length of the cortical shell 0.22, breadth 0.1; length of the medullary shell 0.07, breadth 0.05.

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

3. Zonarium octangulum, n. sp. (Pl. 50, fig. 9).

Cortical shell octangular, one and a fourth times as long as broad, with eight strong conical spines on the eight corners; these are separated by four deep constrictions on the poles of the principal and transverse axes, and by four truncated planes on the poles of the crossed diagonal axes between the former. Sagittal constriction twice as long as the hexagonal medullary shell. Four cupolas kidney-shaped or nearly pentagonal.

Dimensions.—Length of the cortical shell 0.15, breadth 0.12; length of the medullary shell 0.07, breadth 0.04.

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

4. Zonarium tetratholium, n. sp.

Cortical shell quadrangular, with four rounded corners. Surface thorny, with sixteen stronger radial spines; eight of these lie in the lateral plane, in the same symmetrical disposition as in the foregoing species; eight others lie on both sides of the lateral plane, opposite in pairs in two crossed diagonal planes, in the same symmetrical disposition as in Tetrapyle octacantha. Sagittal constriction three times as long as the lentelliptical medullary shell. Four cupolas obliquely elliptical.

Dimensions.—Length of the cortical shell 0.16, breadth 0.12; length of the medullary shell 0.04, breadth 0.03.

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

Genus 302. Zoniscus,^[38] n. gen.

Definition.—Zonarida with six dome-shaped chambers of the cortical shell, separated by three annular constrictions (one sagittal and two transverse, parallel to the equatorial plane).

The genus Zoniscus differs from Zonarium as well as from Zonidium by the development of the transverse girdle, which is not constricted, but on the contrary prominently vaulted in the equatorial plane. Therefore both wings of the transverse girdle form here two opposite lateral or "equatorial cupolas," as in Amphitholus. These are separated from four other domes (the "corner cupolas") by two transverse annular constrictions, which correspond to the free edges of the original transverse girdle. The corner domes of each pair are separated from each other by the sagittal septum.

1. Zoniscus rectangulus, n. sp.

Cortical shell nearly rectangular, with rounded corners, nearly one and a half times as long as broad. Surface thorny, without larger radial spines. Sagittal constriction scarcely half as long as the hexagonal medullary shell. Both equatorial cupolas (or wings of the transverse girdle) scarcely half as large as the four corner cupolas.

Dimensions.—Length of the cortical shell 0.15, breadth 0.11; length of the medullary shell 0.07, breadth 0.045.

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

2. Zoniscus hexathalamus, n. sp.

Cortical shell nearly elliptical, one and a third times as long as broad. Surface nearly smooth, without radial spines. Sagittal constriction three times as long as the lentelliptical medullary shell. Both equatorial cupolas about as large as the four corner cupolas.

Dimensions.—Length of the cortical shell 0.12, breadth 0.09; length of the medullary shell 0.035, breadth 0.025.

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

3. Zoniscus tetracanthus, n. sp. (Pl. 50, fig. 10).

Cortical shell nearly quadrangular, one and a half times as long as broad, with four prominent corners, from which arise in the lateral plane four strong, three-sided pyramidal radial spines (opposite in pairs in two crossed diagonal axes). Surface thorny, with exception of the concave lateral sides. Sagittal constriction two and a half times as long as the hexagonal medullary shell. Both equatorial cupolas scarcely half as large as the four corner cupolas.

Dimensions.—Length of the cortical shell 0.18, breadth 0.12; length of the medullary shell 0.07, breadth 0.04.

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

4. Zoniscus octacanthus, n. sp.

Cortical shell nearly four-sided, prismatic, one and a third times as long as broad, with spiny surface. Eight longer thin radial spines opposite in pairs in two crossed diagonal planes (as in Tetrapyle octacantha). Sagittal constriction two and a half times as long as the hexagonal medullary shell. Both equatorial cupolas somewhat larger than the four corner cupolas.

Dimensions.—Length of the cortical shell 0.16, breadth 0.12; length of the medullary shell 0.055, breadth 0.04.

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

5. Zoniscus hexatholius, n. sp. (Pl. 50, fig 11).

Cortical shell nearly rectangular, with four rounded corners and deep sagittal constriction, one and a fourth times as long as broad with thorny surface. Twelve longer edged radial spines; eight opposite in pairs in two crossed diagonal planes (as in the foregoing species), four others in the lateral plane, opposite in pairs on both sides of the sagittal constriction, which is scarcely twice as long as the hexagonal, in the equatorial plane constricted medullary shell. Both equatorial cupolas nearly of the same size as the four corner cupolas.

Dimensions.—Length of the cortical shell 0.16, breadth 0.13; length of the medullary shell 0.07, breadth 0.04.

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

Genus 303. Zonidium,^[39] n. gen.

Definition.—Zonarida with eight dome-shaped chambers of the cortical shell, separated by four annular constrictions (one sagittal, one transverse, and two others parallel to the latter).

The genus Zonidium must be regarded as a Zonarium, in which the four cupolas (in the quadrants of the lateral plane) are halved by diagonal beams or latticed septa, lying opposite in pairs in two crossed diagonal planes. Therefore the number of the septa (four) and the domes (eight) is here doubled. Among the eight cupolas we distinguish four median (on both sides of the sagittal plane) and four lateral (on both sides of the equatorial plane); both groups are of different size and form. Probably Zonidium is derived from Zonarium by lattice-connection between the eight diagonal wing-spines, which in both species of this genus are present, the same as in Tetrapyle octacantha.

1. Zonidium octostylium, n. sp.

Cortical shell nearly quadrangular, with rounded corners and thorny surface. Eight long and thin radial spines on both sides of the lateral plane opposite in pairs and lying in two crossed diagonal planes (as in Tetrapyle octacantha). Sagittal constriction three times as long as the lentelliptical medullary shell. Four medial cupolas (on both sides of the sagittal plane) somewhat larger than the four lateral cupolas (on both sides of the equatorial plane).

Dimensions.—Length of the cortical shell 0.15, breadth 0.12; length of the medullary shell 0.05, breadth 0.03.

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

2. Zonidium octotholium, n. sp. (Pl. 50, fig. 12).

Cortical shell nearly octangular, with spiny surface; twenty long and stout radial spines between numerous smaller spines; eight wing-spines opposite in pairs in two crossed diagonal planes (as in the preceding species); twelve other strong spines in the lateral plane (four longer opposite in pairs on the poles of the principal and transverse axes, eight others smaller, alternating between these and the diagonal spines). Sagittal constriction twice as long as the hexagonal medullary shell. Four median cupolas somewhat smaller than the four lateral cupolas.

Dimensions.—Length of the cortical shell 0.18, breadth 0.15; length of the medullary shell 0.07, breadth 0.05.

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

Family XXIX. Lithelida, Haeckel (Pl. 49, figs. 1-7).

Lithelida, Haeckel, 1862, Monogr. d. Radiol., p. 515.

Definition.—Larcoidea with symmetrical spiral shell, divided by the spiral plane into two symmetrical halves; all windings of the spiral lie in this plane. Primordial chamber either simple or Larnacilla-shaped.

The family Lithelida comprises all those Larcoidea in which the growth of the latticed shell is spirally winding in one plane, Nautilus-like. They agree in the spiral growth with the following family. But in the Streblonida the spiral is screw-shaped, ascending (like Helix). Therefore in these latter the geometrical fundamental form of the shell is asymmetrical or "dysdipleural," whereas in the Lithelida bilateral-symmetrical or "eudipleural." The lentelliptical or nearly spherical shell may be divided by a median section into two symmetrical halves; the right half is the mirror image of the left half.

When in 1862 I founded the family Lithelida in my Monograph (p. 515), I knew only one genus, Lithelius, with two species. The rich material of the Challenger collection contains a great number of similar spirally constructed Larcoidea, so that at the present time we may distinguish at least six genera. These belong to two different subfamilies, which may possibly be afterwards better separated as families. The first subfamily, Spiremida, possess a simple, spherical or subspherical, medullary shell; the second subfamily, Larcospirida, possess a trizonal or Larnacilla-shaped medullary shell. No doubt these latter must be derived from Pylonida, as we observe all stages of development starting from a simple Trizonium; but perhaps also the Spiremida have the same origin, their simple, spherical or subspherical, medullary shell being derived from a trizonal or Larnacilla-shaped medullary shell by reduction.

The general appearance in both subfamilies of the Lithelida is quite the same, and it requires a careful study of the medullary shell to distinguish certainly the Spiremida from the Larcospirida. This distinction is often not easy, particularly in the larger forms; the shell is often very opaque and difficult to understand. Only in one position, if the spiral axis be parallel to the axis of the eye of the observer, and the spiral plane be therefore fully seen in the optical plane of the microscope, the spiral line (or the axial section of the latticed spiral lamella) is distinctly observed; in all other positions the figure of the spiral is more or less indistinct, and the whole microscopical image often quite intricate and confused. The sufficient study of this family requires therefore the contemplation of the shell from different sides, and is the more difficult, as the variability of the Lithelida—as of the Pylonida—is extraordinarily great.

The description which I gave of Lithelius (1862) in my Monograph is in some points erroneous, and was afterwards (1879) corrected by R. Hertwig, who explained particularly the near relation of it to Tetrapyle. Indeed the intermediate forms between the Lithelida and the Pylonida are so numerous and so evident in all stages of development, that the derivation of the former (at least of the Larcospirida) from the latter is quite clear. The analogy between the structure of the Lithelida and the calcareous (foraminiferous) Alveolinida is not so complete as I supposed it to be in my Monograph (1862); particularly the formation of the small chambers between the turnings of the spiral lamella is much more complete in the Alveolinida than in the Lithelida.

The cortical shell of all Lithelida has the same geometrical fundamental form as Nautilus or as the nautiloid Polythalamia (Polystomella, Nummulites, &c.); therefore the shell is dipleural, being divided by the median plane into two symmetrical lateral halves. Since the spiral line lies in the median plane, we will call it the spiral plane; it separates the right half from the left. The axis of the body, around which the spiral turns (without touching it), is the spiral axis. The latticed part of the cortical shell, which turns around them, is the spiral lamella. Only in one genus of our family, viz., Tholospira, are the spiral axis, the lateral axis, the spiral plane, and the sagittal plane quite as in Nautilus. In all other genera this disposition is different or is uncertain. This depends on the different part of the cortical shell, from which the spiral growth begins. In this respect we can distinguish four different modes.

In the Larcospirida (or the Lithelida with Larnacilla-shaped medullary shell) the spiral growth exhibits four quite different forms. It begins here with Larcospira, in which already the first cortical girdle of the Diplozonaria determines the spiral growth; one wing of this girdle, the transverse girdle of Amphipyle, grows more swiftly than the other, overgrows it, and thus turns around the principal axis. In Pylospira the first or transverse girdle is already perfectly formed (as in Amphipyle), and the spiral growth is introduced by the second or lateral girdle of Tetrapyle; one wing of it (the right or the left) grows more swiftly than the other, overgrows it, and thus turns around the sagittal axis. In Tholospira also the second girdle is complete, and the spiral growth begins from the third or sagittal girdle. One of its wings grows more swiftly than the other, overgrows it, and thus turns around the transverse axis. Consequently we see that each of the three dimensive planes of the lentelliptical Larcoid-body may be the spiral plane: in Larcospira the transverse plane, in Pylospira the lateral plane, in Tholospira the sagittal plane. Correspondingly the spiral axis in the first genus is the principal, in the second the sagittal, in the third the transverse axis of the central Larnacilla-shell. Therefore in these three genera the spiral plane is the plane of the latticed girdle, which determines the spiral growth, one of both its wings overgrowing the other.

In each of the three above mentioned genera the spiral may be simple or double; it remains simple if only one of both wings of the turning girdle overgrow the other, and this latter remain a simple half girdle (or tube-like wing). Whereas the spiral becomes double if the second wing of the girdle afterwards follow the example of the first wing and now turn around it in the same direction. As this happens in all three genera, we can subdivide them into six subgenera.

A quite peculiar form of spiral growth is produced in Spironium, in which the direction of growth in both lateral wings of the transverse girdle is inverse from the beginning. The left wing grows against the posterior, the right wing against the anterior pole of the principal axis, turning around it in crossed, eight-like spirals. The whole shell afterwards assumes a lentelliptical form.

Commonly between the embracing spiral turnings or convolutions a great number of radial beams is developed, irregularly disposed and often branching; they support the thin spiral lamellæ and give to the whole shell more solidity. Often these beams form imperfect radial septa, by which the spiral cavity of the turnings is divided into a variable number of chambers. But these chambers never become so regular and perfect as in the analogous nautiloid Polythalamia.

In many Lithelida the growth of the shell reaches a certain limit, concluding with the formation of a superficial latticed lamella of lentelliptical or nearly spherical form. In many other forms of the family this seems not to be the case; but these may possibly be younger forms, afterwards reaching the same limit.

The network of the shell in the Lithelida is commonly quite irregular, and so variable that its special conformation has usually no value in the determination of the species. The surface of the shell is often covered with radial spines, which are sometimes arborescent.

The central capsule seems always to preserve the same lentelliptical form (or triaxial ellipsoid) as in all other Larcoidea. With the increase of growth it encloses successively a larger part of the spiral cortical shell, but on the outside is constantly protected by the last turnings of the spiral, or by the lattice-lamella of the surface.

Synopsis of the Genera of Lithelida.

II. Subfamily Spiremida. Central medullary shell simple, spherical or lentelliptical.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Surface of the cortical shell smooth or thorny, withou radial spines,	304. Spirema.
		Surface of the cortical shell covered with numerous simple or branched radial spines,	305. Lithelius.
II. Subfamily Larcospirida. Central medullary shell double, trizonal or Larnacilla-shaped.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	The transverse girdle turns around the principal axis,	306. Larcospira.
		The lateral girdle turns around the sagittal axis,	307. Pylospira.
		The sagittal girdle turns around the transverse axis,	308. Tholospira.
		Both wings of the transverse girdle turn around the principal axis in an opposite diagonal direction,	309. Spironium.

Subfamily 1. Spiremida, Haeckel, 1881, Prodromus, p. 464.

Definition.—Lithelida with simple, spherical or subspherical, medullary shell.

Genus 304. Spirema,^[40] Haeckel, 1881, Prodromus, p. 464.

Definition.—Lithelida with simple, spherical or subspherical, medullary shell, and lentelliptical or subspherical, spirally constructed cortical shell; surface smooth or thorny, without radial spines.

The genus Spirema begins the series of the Spiremida, or of those Lithelida in which the medullary shell presents a simple latticed sphere or ellipsoid, never composed of a double, trizonal or Larnacilla-shaped shell. In the present state of our knowledge we cannot say whether this simple medullary shell be a primary formation, or effected by secondary means, by reduction of a double Larnacilla-shaped medullary shell, which is constantly found in the Larcospirida. The species of this genus (as of all Lithelida) are difficult to distinguish, are transformistic, and incline very much to variations and abnormalities. The spiral may be simple or double.

Subgenus 1. Spiremarium, Haeckel.

Definition.—Spiral convolutions of the cortical shell simple.

1. Spirema lentellipsis, n. sp.

Cortical shell lentelliptical, with smooth surface; proportion of its three dimensive axes = 4 : 5 : 6. In the median plane are visible four perfect turnings of the simple spiral, the breadth of which gradually increases towards the third convolution, finally decreasing; the broadest (third) turning three times as broad as the simple spherical medullary shell.

Dimensions.—Length of the lentelliptical cortical shell 0.18, breadth 0.15, height 0.12; diameter of the spherical medullary shell 0.02.

Habitat.—North Atlantic, Station 353, surface.

2. Spirema melonia, n. sp. (Pl. 49, fig. 1).

Cortical shell nearly spherical, with smooth surface; proportion of its three dimensive axes = 1.4 : 1.5 : 1.6. In the median plane are visible three perfect turnings of the simple spiral, all of the same breadth as the simple spherical medullary shell; the breadth of each convolution somewhat greater at the poles of the principal than at the poles of the sagittal axis.

Dimensions.—Length of the shell 0.16, breadth 0.15, height 0.14; medullary shell 0.018.

Habitat.—Pacific, central area, Station 271, surface.

3. Spirema flustrella, Haeckel.

Flustrella haliomma, Ehrenberg (1861), Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, p. 293, Taf. ii. fig. 6.

Cortical shell egg-shaped, with thorny surface; proportion of its three axes = 4 : 5 : 6. In the median plane are visible three perfect turnings of the simple spiral, the first and second of about the same breadth as the simple spherical medullary shell, the third suddenly increasing, and finally three to four times as broad. Network of the surface irregular, with roundish pores.

Dimensions.—Length of the shell 0.2, breadth 0.17, height 0.14; medullary shell 0.013.

Habitat.—North Atlantic, Greenland, 1000 fathoms, Ehrenberg; Færöe Channel, John Murray.

Subgenus 2. Spiremidium, Haeckel.

Definition.—Spiral convolutions of the cortical shell double.

4. Spirema diplospira, n. sp.

Cortical shell lentelliptical, with smooth surface; proportion of its three dimensive axes = 6 : 7 : 8. In the median plane are visible three perfect turnings of a double spiral, the breadth of which gradually increases; the broadest (third) convolution three times as broad as the simple lentelliptical medullary shell.

Dimensions.—Length of the shell 0.24, breadth 0.21, height 0.18; medullary shell 0.02.

Habitat.—Tropical Pacific, Philippines, Station 200, depth 250 fathoms.

5. Spirema subglobosum, n. sp.

Cortical shell nearly spherical, with thorny surface; proportion of its three axes = 2 : 2.1 : 2.2. In the median plane are visible two perfect turnings of a double spiral, the breadth of which in the second convolution is four times as great as that of the first convolution and the simple spherical medullary shell.

Dimensions.—Length of the shell 0.22, breadth 0.21, height 0.2; medullary shell 0.02.

Habitat.—Tropical Atlantic, off Sierra Leone, Station 348, depth (2450) fathoms.

Genus 305. Lithelius,^[41] Haeckel, 1862, Monogr. d. Radiol., p. 519.

Definition.—Lithelida with simple, spherical or subspherical, medullary shell, and lentelliptical or subspherical, spirally constructed cortical shell; surface covered with numerous, simple or branched, radial spines.

The genus Lithelius, founded by me in 1862, and represented by two Mediterranean species, was at that time the only known form of this family, which now contains six genera and twenty-seven species. It differs from the foregoing Spirema in the possession of numerous radial spines on the surface. These may be either simple or branched. The spiral may be simple or double, and according to this latter modification we distinguish two different subgenera.

Subgenus 1. Lithospira, Haeckel.

Definition.—Spiral convolutions of the cortical shell simple.

1. Lithelius spiralis, Haeckel.

Lithelius spiralis, Haeckel, 1862, Monogr. d. Radiol., p. 519, Taf. xxvii. figs. 6, 7.

Cortical shell lentelliptical, one and a third times as long as broad, covered with very numerous (one hundred to one hundred and fifty or more) simple, bristle-shaped radial spines, about as long as the shell. Spiral turnings simple, all nearly of the same breadth and scarcely broader than the simple spherical medullary shell.

Dimensions.—Length of the cortical shell (with six spiral convolutions) 0.15, breadth 0.13; diameter of the medullary shell 0.012.

Habitat.—Mediterranean, Messina, Haeckel, surface; Atlantic, Stations 348 to 353, surface.

2. Lithelius primordialis, R. Hertwig.

Lithelius primordialis, R. Hertwig, 1879, Organism. d. Radiol., p. 54, Taf. vi. figs. 4, 4a.

Cortical shell subspherical, covered with numerous simple, bristle-shaped radial spines, longer than the shell. Spiral turnings simple, with gradually increasing breadth, so that the beginning of the third spiral is twice as broad as the first and as the simple spherical medullary shell.

Dimensions.—Diameter of the cortical shell (with two spiral convolutions) 0.12; diameter of the medullary shell 0.02.

Habitat.—Mediterranean, Messina, R. Hertwig, surface.

3. Lithelius alveolina, Haeckel, 1862.

Lithelius alveolina, Haeckel, 1862, Monogr. d. Radiol., p. 520, Taf. xxvii. figs. 8, 9.

Cortical shell spherical, covered with simple, very numerous (two hundred to three hundred or more), short, bristle-shaped radial spines, scarcely half as long as the radius of the shell. Spiral turnings simple, with gradually increasing breadth, so that the beginning of the third spiral is three times as broad as the first and as the simple spherical medullary shell.

Dimensions.—Diameter of the cortical shell (with four spiral convolutions) 0.2; diameter of the medullary shell 0.01.

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

4. Lithelius capreolus, n. sp.

Cortical shell lentelliptical, one and a fourth times as long as broad, covered with numerous (eighty to one hundred and twenty or more) short, branched radial spines, about half as long as the radius of the shell; each spine once or twice dichotomous, with curved divergent branches. Spiral turnings simple, with gradually increasing breadth, so that the beginning of the third spiral is twice as broad as the first, and as the simple spherical medullary shell.

Dimensions.—Length of the cortical shell (with four spiral convolutions) 0.18, breadth 0.14; diameter of the medullary shell 0.015.

Habitat.—Pacific, central area, Station 274, surface.

Subgenus 2. Drymospira, Haeckel, 1881, Prodromus, p. 464.

Definition.—Spiral convolutions of the cortical shell double.

5. Lithelius solaris, n. sp. (Pl. 49, fig. 2).

Cortical shell spherical, covered with simple, very numerous (two hundred to three hundred) bristle-shaped radial spines, longer than the diameter of the shell. Spiral turnings double, both of the same breadth, gradually increasing with the growth of the shell and several times surpassing the diameter of the simple spherical medullary shell. (Pl. 49, fig. 2, exhibits only the first convolutions in the centre of the shell.)

Dimensions.—Diameter of the cortical shell (with four spiral convolutions) 0.18; diameter of the medullary shell 0.02.

Habitat.—Pacific, central area, Stations 266 to 272, surface and in various depths.

6. Lithelius arborescens, n. sp.

Cortical shell lentelliptical, one and a half times as long as broad, covered with numerous (fifty to eighty or more) branched radial spines, about as long as the greatest diameter of the shell; each spine with two to four lateral branches, which are again branched or dichotomous. Spiral turnings double, both of little different breadth, which increases considerably with the growth of the shell, so that the third turn is four times as broad as the simple spherical medullary shell.

Dimensions.—Length of the cortical shell (with three spiral convolutions) 0.18, breadth 0.12; diameter of the medullary shell 0.01.

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

Subfamily 2. Larcospirida, Haeckel.

Definition.—Lithelida with double, trizonal, or Larnacilla-shaped medullary shell.

Genus 306. Larcospira,^[42] n. gen.

Definition.—Lithelida with double, trizonal, or Larnacilla-shaped medullary shell; cortical shell subspherical or lentelliptical, constructed of a simple or double spiral of the transverse girdle (or primary cortical girdle); the spiral lamella revolving around the principal axis.

The genus Larcospira begins the interesting series of the Larcospirida, or of those Lithelida in which the medullary shell is formed by a trizonal or Larnacilla-shaped lattice-shell, and the cortical shell by spiral turnings of one of the three girdles, which compose the cortical shell of the Pylonida. In Larcospira, as the oldest and most simple form of Larcospirida, the spiral is formed by the transverse girdle, or the first girdle of the Diplozonaria, the only cortical girdle of Amphipyle. If in this genus one of both wings of the transverse girdle grow stronger than the other and overgrow the latter, turning around the principal axis, we reach the characteristic form of Larcospirema, the first subgenus of Larcospira; but if afterwards the second wing follow the example of the first, and overgrow it from the other side, we reach the typical form of the second subgenus, Larcospironium. In this latter subgenus the spiral becomes double, whilst in the former it remains simple.

Subgenus 1. Larcospirema, Haeckel.

Definition.—Spiral convolutions or turns of the cortical shell simple; only one single wing of the transverse girdle turning around the principal axis.

1. Larcospira lentelliptica, n. sp.

Cortical shell with smooth surface, four times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a half times as long as broad, without constrictions. One lateral wing of the transverse girdle is more strongly developed and turns around the other in two to three simple spiral turns.

Dimensions.—Length of the cortical shell 0.2, breadth 0.16; length of the medullary shell 0.05, breadth 0.04.

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

2. Larcospira quadrangula, n. sp. (Pl. 49, fig. 3).

Cortical shell with thorny surface, three times as long as the lentelliptical medullary shell. Perimeter of the lateral plane nearly quadrangular, with four rounded corners (on the poles of two crossed diagonal axes), one and a third times as long as broad, with one sagittal constriction at the poles of the principal axis. One lateral wing of the transverse girdle turns around the other in one and a half to two simple spiral turns.

Dimensions.—Length of the cortical shell 0.18, breadth 0.14; length of the medullary shell 0.06, breadth 0.04.

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

3. Larcospira sexangula, n. sp.

Cortical shell with spiny surface, four times as long as the hexagonal medullary shell. Perimeter of the lateral plane nearly hexagonal, one and a half times as long as broad, with six rounded corners (two on the poles of the principal axis, four on the poles of two crossed diagonal axes), with three slight ring-like constrictions. One lateral wing of the transverse girdle turns around the other in two to two and a half simple spiral turns.

Dimensions.—Length of the cortical shell 0.24, breadth 0.16; length of the medullary shell 0.06, breadth 0.04.

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

Subgenus 2. Larcospironium, Haeckel.

Definition.—Spiral convolutions or turns of the cortical shell double; both wings of the transverse girdle turning around the principal axis.

4. Larcospira oliva, n. sp.

Cortical shell with smooth surface, six times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a fourth times as long as broad, without constrictions. Both lateral wings of the transverse girdle turn round one another and form one and a half to two double spiral turns.

Dimensions.—Length of the cortical shell 0.25, breadth 0.2; length of the medullary shell 0.04, breadth 0.035.

Habitat.—Antarctic Ocean, Station 157, depth 1950 fathoms.

Genus 307. Pylospira,^[43] n. gen.

Definition.—Lithelida with double, trizonal or Larnacilla-shaped medullary shell; cortical shell subspherical or lentelliptical, constructed of a single or double spiral of the lateral girdle (or second cortical girdle); the spiral lamella revolving round the sagittal axis.

The genus Pylospira follows after Larcospira as the second genus of Larcospirida; but in this latter the spiral of the cortical shell is formed by the transverse girdle (or the first lattice-girdle of the Diplozonaria), whilst in Pylospira it is produced by the lateral girdle, or the second lattice-girdle of that group. Therefore Pylospira may be derived phylogenetically from Tetrapyle in the same manner as Larcospira from Amphipyle. Whilst in this latter the first cause of the spiral turning, the unequal growth of both girdle-wings, proceeds from the transverse girdle, in Pylospira it proceeds from the lateral girdle. One of its wings overgrows the other, turning around the sagittal axis. If the second wing do not become developed, the spiral remains simple and represents the subgenus Pylospirema; but if afterwards the second wing follow the example of the first and overgrow it from the other side, we reach the typical form of the second subgenus, Pylospironium, with a double spiral.

Subgenus 1. Pylospirema, Haeckel.

Definition.—Spiral convolutions or turns of the cortical shell simple, only one single wing of the lateral girdle turning around the sagittal axis.

1. Pylospira tetrapyle, n. sp.

Cortical shell with thorny surface, five times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a half times as long as broad. Four internal gates (as in Tetrapyle, between the complete lateral wings of the transverse girdle) kidney-shaped. One principal wing of the lateral girdle turns around the other in one and a half to two simple spiral turns.

Dimensions.—Length of the cortical shell 0.21, breadth 0.15; length of the medullary shell 0.04, breadth 0.03.

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

2. Pylospira octopyle, n. sp. (Pl. 49, fig. 4).

Cortical shell with thorny surface, three times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical or nearly hexagonal, with four rounded corners (on the poles of two crossed diagonal axes), one and a third times as long as broad. Eight internal egg-shaped gates (as in Octopyle), between the complete lateral wings of the transverse girdle, and two axial beams in the principal axis. One single wing of the lateral girdle turns around the other in two to three simple spiral turns.

Dimensions.—Length of the cortical shell 0.18, breadth 0.14; length of the medullary shell 0.06, breadth 0.035.

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

Subgenus 2. Pylospironium, Haeckel.

Definition.—Spiral convolutions or turns of the cortical shell double; both wings of the lateral girdle turning around the sagittal axis.

3. Pylospira cymbium, n. sp.

Cortical shell with smooth surface, seven times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a third times as long as broad. Four internal kidney-shaped gates between the complete lateral wings of the transverse girdle (as in Tetrapyle). Both principal wings of the lateral girdle turn round one another in two to two and a half double spiral turns.

Dimensions.—Length of the cortical shell 0.22, breadth 0.17; length of the medullary shell 0.03, breadth 0.025.

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

Genus 308. Tholospira,^[44] n. gen.

Definition.—Lithelida with double, trizonal or Larnacilla-shaped medullary shell; cortical shell subspherical or lentelliptical constructed of a simple or double spiral of the sagittal girdle (or third cortical girdle); the spiral lamella revolving around the transverse axis.

The genus Tholospira represents the third genus of Larcospirida. Whilst the spiral growth of the cortical shell is produced in Larcospira by the first (transverse) girdle of the Diplozonaria, in Pylospira by the second (lateral) girdle, in Tholospira it is effected by the third or sagittal girdle, which we found complete in Pylonium. If in this genus one wing of the sagittal girdle overgrow the other remaining one and turn around the transverse axis, we get Tholospirema, the first subgenus of our genus, with simple spiral; but if afterwards the second wing follow the example of the first, and overgrow it from the other side, we get Tholospironium, with double spiral.

Subgenus 1. Tholospirema, Haeckel.

Definition.—Spiral convolutions or turns of the cortical shell simple, only one single wing of the sagittal girdle turning around the transverse axis.

1. Tholospira nautiloides, n. sp.

Cortical shell with smooth surface, five times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a half times as long as broad. Four internal kidney-shaped gates (between the lateral wings of the transverse girdle, as in Tetrapyle). One wing of the sagittal girdle turns around the other in two to two and a half simple spiral turns.

Dimensions.—Length of the cortical shell 0.24, breadth 0.18; length of the medullary shell 0.05, breadth 0.04.

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

2. Tholospira spinosa, n. sp.

Cortical shell covered with numerous (sixty to eighty or more) simple, bristle-like radial spines, about the length of the shell. Perimeter of the lateral plane nearly quadrangular, with four rounded corners (on the poles of two crossed diagonal axes), one and a half times as long as broad. Eight internal egg-shaped gates (between the lateral wings of the transverse girdle and two axial beams in the principal axes, as in Octopyle). One wing of the sagittal girdle turns around the other in two to three simple spiral turns.

Dimensions.—Length of the cortical shell 0.27, breadth 0.18; length of the medullary shell 0.04, breadth 0.03.

Habitat.—South Pacific, Station 288, surface.

3. Tholospira dendrophora, n. sp. (Pl. 49, fig. 6).

Cortical shell covered with numerous (forty to fifty or more) branched radial spines, about half as long as the shell; each spine with two to six dichotomous branches. Perimeter of the lateral plane elliptical, one and a third times as long as broad. Eight internal egg-shaped gates, as in the foregoing species. One single wing of the sagittal girdle turns around the other in three to four spiral turns.

Dimensions.—Length of the cortical shell 0.22, breadth 0.17; length of the medullary shell 0.05, breadth 0.04.

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

Subgenus 2. Tholospironium, Haeckel.

Definition.—Spiral convolutions of the cortical shell double; both wings of the sagittal girdle turning around the transverse axis.

4. Tholospira hystrix, n. sp.

Cortical shell covered with numerous (sixty to eighty or more) simple conical spines, about half as long as the shell. Perimeter of the lateral plane hexagonal, one and a half times as long as broad. Four internal kidney-shaped gates, as in Tetrapyle. Both wings of the sagittal girdle turn round one another in two to two and a half double spiral turns.

Dimensions.—Length of the cortical shell 0.21, breadth 0.14; length of the medullary shell 0.04, breadth 0.03.

Habitat.—North Atlantic, Station 354, surface.

5. Tholospira cervicornis, n. sp. (Pl. 49, fig. 5).

Cortical shell covered with numerous (forty to fifty or more) branched radial spines; each spine antler-shaped, about as long as the medullary Larnacilla-shell, with eight to twelve dichotomous branches (similar to Cromyodrymus abietinus, Pl. 30, fig. 6). Perimeter of the lateral plane elliptical, one and a third times as long as broad. Four internal kidney-shaped gates, as in Tetrapyle. Both wings of the sagittal girdle turn round one another in one and a half to two double spiral turns.

Dimensions.—Length of the cortical shell 0.2, breadth 0.15; length of the medullary shell 0.03, breadth 0.025.

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

Genus 309. Spironium,^[45] n. gen.

Definition.—Lithelida with double, trizonal or Larnacilla-shaped medullary shell; cortical shell subspherical or lentelliptical, constructed of two crossed spirals, which arise from both lateral wings of one girdle (commonly the lateral girdle) and revolve in an opposite diagonal direction around the principal axis.

The genus Spironium differs in a very remarkable manner from all foregoing Lithelida, and is distinguished by a quite peculiar mode of growth. It is most nearly allied to Larcopyle, and may, like this, be derived from Amphipyle (or rather from Larnacilla, beginning to transform into Amphipyle). But whilst in Larcopyle one of the two wings of the lateral girdle overgrows the other in the direction of the transverse axis (turning around the principal axis), here in Spironium both lateral wings begin at the same time to grow out from the lateral sides of the Larnacilla-shaped medullary shell; the most remarkable thing is, however, that the direction of growth in the wings is diverse from the beginning: the left wing grows downwards and turns around the lower (aboral) pole of the principal axis, the right wing grows upwards and turns around the upper (oral) pole of the same axis. Thus both wings of the lateral girdle are crossed in diagonal axes, and with increasing growth one overgrows the other in the direction of these diagonals, so as to resemble the figure 8 in shape. The open gates remaining between the turnings of the girdle become afterwards closed on the surface by irregular lattice-work, and so the whole cortical shell assumes finally a spherical, ellipsoidal, or lentelliptical form. Its surface sometimes becomes covered with simple or branched radial spines. In the interior the eight characteristic egg-shaped gates of Octopyle are commonly (or constantly?) visible, two strong radial beams in the principal axis arising from the poles of the lentelliptical medullary shell.

Subgenus 1. Spironetta, Haeckel.

Definition.—Surface of the shell smooth or rough, but not with radial spines.

1. Spironium octonium, n. sp. (Pl. 49, fig. 7).

Cortical shell lentelliptical, its breadth (or transverse axis) surpassing considerably the length (or the principal axis). Surface thorny and somewhat hump-backed. The spiral wings of the transverse girdle have about the same breadth as the eight internal gates between them and the axial beams.

Dimensions.—Length of the cortical shell (or principal axis) 0.15, breadth (or transverse axis) 0.2; length of the medullary shell 0.05, breadth 0.04.

Habitat.—South Atlantic, west of Tristan da Cunha, Station 332, depth 2200 fathoms.

2. Spironium diagonale, n. sp.

Cortical shell nearly spherical, four times as great as the subspherical medullary shell. Surface rough. The spiral wings of the transverse girdle about half as broad as the eight internal gates between them and the axial beams.

Dimensions.—Diameter of the cortical shell 0.16, of the medullary shell 0.04.

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

Subgenus 2. Spironilla, Haeckel.

Definition.—Surface of the shell covered with simple or branched radial spines.

3. Spironium spinosum, n. sp.

Cortical shell subspherical, five times as great as the subspherical medullary shell. Surface covered with numerous (sixty to eighty or more) simple, bristle-like radial spines, longer than the shell. The spiral wings of the transverse girdle of about the same breadth as the eight internal gates between them and the axial beams.

Dimensions.—Diameter of the cortical shell 0.2, of the medullary shell 0.04.

Habitat.—Pacific, central area, Station 274, surface.

4. Spironium arbustum, n. sp.

Cortical shell lentelliptical, its breadth surpassing its length considerably. Surface covered with numerous (forty to sixty or more) thin radial spines, about as long as the greatest diameter of the shell; each spine with two to six lateral branches, which are either simple or again branched (similar to Cromyodrymus abietinus, Pl. 30, fig. 6). The spiral wings of the transverse girdle only half as broad as the eight internal gates between them and the strong beams of the principal axis.

Dimensions.—Length of the cortical shell 0.12, breadth 0.15; length of the hexagonal medullary shell 0.05, breadth 0.04.

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

Family XXX. Streblonida, n. fam. (Pl. 49, figs. 8, 9).

Definition.—Larcoidea with asymmetrical, spiral, polythalamous shell, composed of a variable number of roundish chambers, which form together an ascending spiral; both halves of the shell unequal. Primordial chamber either simple or Larnacilla-shaped.

The family Streblonida comprises those Larcoidea in which a number of chambers is arranged in an ascending spiral, round a simple or trizonal primordial chamber, like winding stairs. They show the same spiral structure as in the foregoing family, but whilst in the Lithelida the spiral line lies in one plane (as in Nautilus), in the Streblonida it ascends like a screw (as in Helix). Therefore the former have the same relation, regarding the spiral structure, to the nautiloid Polythalamia as the latter to the turbinoid Foraminifera. Indeed the single forms of Streblemida repeat in their special structure the characteristic genera of Turbinoida, such as Globigerina, Rosalina, Pulvinulina, Hastigerina, &c. As in these calcareous turbinoid Foraminifera, so also in the analogous siliceous Streblonida the distinction of species is very difficult and open to many objections.

The number of species in this family is very small; all are rare and for the most part very opaque and difficult to understand, so that the following distinction of a dozen species can have only a provisional value. To get a complete idea of their peculiar structure, the shell must be turned and observed from different sides, and thus their full study requires yet much time and work. There are to be found evident transitional forms between them and the Lithelida on the one hand and the Soreumida on the other. Besides this, most species of Streblonida seem to have more inclination to individual varieties and abnormalities than the majority of the other Radiolaria.

The general form of the whole shell is in the Streblonida sometimes more egg-shaped or even subspherical, at other times more top-like or conical, sometimes nearly discoidal. The height of the shell (or the vertical axis of the ascending spiral) is occasionally larger, at other times smaller than the breadth (or the greatest horizontal diameter, perpendicular to the height). Some very flat forms seem to approach the Lithelida. With regard to the internal screw-formation, the shell of all Streblonida is asymmetrical.

The number of the aggregated incomplete chambers is commonly between ten and twenty, but ascends sometimes to thirty, forty, or more. Sometimes the size of all the chambers is nearly the same, sometimes they increase gradually, occasionally also very rapidly. The primordial chamber (or the first and oldest) seems to be commonly the smallest, and inversely, the last and youngest chamber, the largest. But sometimes (in Streblopyle) also the contrary may be the case. The form of the single chambers is very variable, from the spherical or hemispherical through all transitions leading to irregular roundish or longish forms. The network is commonly irregular, with small roundish pores of different sizes, but sometimes also regular, circular. The surface of the shell is commonly smooth or rough, rarely covered with radial spines. In most species the reticulation and particularly the separation of the chambers is more or less incomplete.

As in the Lithelida, so also in the Streblonida we can distinguish two subfamilies. In the Streblacanthida (Streblonia, Streblacantha) the primordial chamber is a simple, spherical, subspherical, or lentelliptical latticed shell. In the Streblopylida (Streblopyle) the primordial chamber is trizonal or Larnacilla-shaped, as in the greater number of Larcoidea, composed of three elliptical latticed girdles of unequal size, perpendicular one to another, and surrounding a simple central chamber. As in the Lithelida, so also here we cannot certainly say whether the former have originated from the latter by reduction of the Larnacilla-shell, or whether both groups be of different origin. The latter is perhaps more probable. This family as well as the foregoing requires a much more careful study than I could give to it.

Synopsis of the Genera of Streblonida.

I. Subfamily Streblacanthida. Primordial chamber simple, spherical or lentelliptical.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Shell without radial spines,	310. Streblonia.
		Shell with radial spines,	311. Streblacantha.
II. Subfamily Streblopylida. Primordial chamber trizonal or Larnacilla-shaped		Shell without radial spines,	312. Streblopyle.

Genus 310. Streblonia,^[46] n. gen.

Definition.—Streblonida with simple, spherical, subspherical, or lentelliptical primordial chamber, beginning the screw-like series of spirally ascending chambers. Surface smooth or thorny, without radial spines.

The genus Streblonia contains those Streblonida in which a variable number of roundish, subspherical, or longish chambers form a screw-like aggregate, beginning with a quite simple primordial chamber. The special order of the complex spiral offers interesting resemblances to different genera of the calcareous Foraminifera, from which I have taken the corresponding name of the species. The whole form of the shell is sometimes more egg-shaped or subspherical, at other times more top-like or conical, occasionally very flat. Its surface is smooth or rough, but not covered with radial spines.

1. Streblonia globigerina, n. sp.

Shell subspherical, thick walled, clustered, with eight to ten nearly spherical chambers, of rapidly increasing size, the tenth chamber about twelve times as broad as the first. Breadth of the shell nearly equal to the height. Pores subregular, circular, hexagonally formed, of about the same breadth as the bars; about sixteen on the breadth of the tenth chamber. (Resembles very much the common Globigerina.)

Dimensions.—Breadth of the shell 0.18, height 0.16.

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

2. Streblonia uvigerina, n. sp.

Shell nearly egg-shaped, clustered, with eight to eleven subspherical chambers of gradually increasing size, the tenth chamber about six times as broad as the first. Breadth of the shell about half its height. Pores of the shell subregular, circular, about twice as broad as the bars; about twenty on the breadth of the tenth chamber. (Resembles some species of Uvigerina.)

Dimensions.—Breadth of the shell 0.11, height 0.23.

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

3. Streblonia polymorphina, n. sp.

Shell egg-shaped, thin walled, with twelve to fourteen roundish chambers of rapidly increasing size, the tenth chamber about seven times as broad as the first. Breadth of the shell about two-thirds of the height. Pores irregular roundish, twice as broad as the bars; about twenty on the tenth chamber. (Resembles certain forms of Polymorphina.)

Dimensions.—Breadth of shell 0.22, height 0.14.

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

4. Streblonia bulimina, n. sp.

Shell nearly egg-shaped, thick walled, clustered, with fourteen to eighteen egg-shaped chambers of rapidly increasing size, the tenth chamber about eight times as broad as the first. Breadth of the shell about two-thirds of the height. Pores irregular, roundish, half as broad as the bars; about twelve on the breadth of the tenth chamber. (Resembles closely Bulimina.)

Dimensions.—Breadth of the shell 0.17, height 0.24.

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

5. Streblonia rosalina, n. sp.

Shell top-shaped or flatly conical, with twelve to sixteen chambers of gradually increasing size, the tenth chamber about four times as broad as the first. Breadth of the shell twice as large as the height. Pores subregular, circular, very small, of the same breadth as the bars; about twelve on the breadth of the tenth chamber. (Resembles some forms of Rosalina.)

Dimensions.—Breadth of the shell 0.27, height 0.13.

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

6. Streblonia planorbulina, n. sp.

Shell very flatly conical, nearly lenticular or discoidal, with twenty to twenty-five chambers of nearly equal size, the tenth chamber a little broader than the first. Breadth of the shell exceeds five to six times the height. Pores subregular, circular, very small, half as broad as the bars; about eight on the breadth of the tenth chamber. (Resembles closely Planorbulina.)

Dimensions.—Breadth of the shell 0.3 to 0.4, height 0.06 to 0.07.

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

7. Streblonia pulvinulina, n. sp.

Shell top-shaped or flatly conical, with thirty to forty chambers of slowly increasing size, the tenth chamber about three times as broad as the first. Breadth of the shell exceeds three times the height. Pores circular, subregular, very small, about one-third as broad as the bars; about thirty in the breadth of the tenth chamber. (Resembles closely Pulvinulina.)

Dimensions.—Breadth of the shell 0.25, height 0.08.

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

Genus 311. Streblacantha,^[47] n. gen.

Definition.—Streblonida with simple, spherical, subspherical, or lentelliptical primordial chamber, beginning the screw-like series of spirally ascending chambers. Surface covered with radial spines.

The genus Streblacantha differs from the nearly allied Streblonia only in the covering of radial spines, and bears therefore the same relation to it as Hastigerina has to Globigerina amongst the similar calcareous Polythalamia.

1. Streblacantha siderolina, n. sp. (Pl. 49, figs. 8, 8a).

Streblonia siderolina, Haeckel, 1883, MS.

Shell flatly conical, with fourteen to sixteen nearly hemispherical chambers of gradually increasing size, the tenth chamber about six times as broad as the first. Breadth of the shell nearly equal to the height. Pores subregular, circular, hexagonally framed, twice as broad as the bars; about nine pores on the breadth of the tenth chamber. Surface covered with numerous short conical radial spines, one-fourth to one-sixth as long as the diameter of the shell.

Dimensions.—Breadth of the shell 0.15, height 0.17.

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

2. Streblacantha calcarina, n. sp.

Shell conical, with sixteen to eighteen roundish chambers of gradually increasing size, the tenth chamber about three times as broad as the first. Breadth of the shell about one and a half times the height. Pores irregular, roundish. Surface covered with numerous strong conical radial spines, about half as long as the diameter of the shell.

Dimensions.—Breadth of the shell 0.24, height 0.17.

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

3. Streblacantha hastigerina, n. sp.

Shell nearly spherical, clustered, with nine to eleven nearly spherical chambers of rapidly increasing size, the tenth chamber about six times as broad as the first. Breadth of the shell nearly equal to the height. Pores subregular, circular, of about the same breadth as the bars. Surface bristly, covered with numerous very thin and long, needle-shaped radial spines, longer than the diameter of the shell. (Resembles closely Hastigerina.)

Dimensions.—Breadth of the shell 0.18, height 0.15.

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

Genus 312. Streblopyle,^[48] n. gen.

Definition.—Streblonida with trizonal lentelliptical medullary shell (composed like Larnacilla of three elliptical dimensive girdles surrounding one simple central primordial chamber). From this begins a screw-like series of spirally ascending chambers. Surface smooth or thorny, without radial spines.

The genus Streblopyle presents externally the same appearance and contour as Streblonia, and is composed like this of a variable number of chambers, ascending screw-like around the axis of the spiral shell. The first or primordial chamber, however, in which the growth begins, is in Streblonia a simple spherical shell, but in Streblopyle a trizonal shell or Larnacilla-shell (compare above, p. 600). The chambers are very incompletely separated, and comparatively much larger, their number much smaller than in Streblonia. The structure in the species of this genus is difficult to understand.

1. Streblopyle helicina, n. sp. (Pl. 49, fig. 9).

Shell helicoid, one and a third times as high as broad, with eight to twelve incomplete semizonal chambers, ascending spirally from the lateral half girdle of the lentelliptical medullary shell, octopyle-shaped, and enveloping it in three to four spiral turnings. The height of the whole cortical shell equals nearly five times the height of the trizonal medullary shell. Pores irregular, roundish. Surface of the shell rough or nearly smooth. (This species seems to be nearly allied to Spironium octonium.)

Dimensions.—Breadth of the spiral cortical shell 0.18, height 0.24; breadth of the medullary shell 0.04, height 0.05.

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

2. Streblopyle spirulina, n. sp.

Shell egg-shaped or nearly spherical, about as high as broad, with eight to nine semizonal chambers, ascending spirally from the subspherical trizonal medullary shell, and enveloping it in four to five turnings. The sixth chamber twice as broad as the trizonal medullary shell. Pores irregular, roundish. Surface of the shell thorny.

Dimensions.—Breadth of the spiral cortical shell 0.27, height 0.25; breadth of the medullary shell 0.05, height 0.06.

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

Family XXXI. Phorticida, Haeckel (Pl. 49, figs. 10, 11).

Phorticida, Haeckel, 1881, Prodromus, p. 464.

Definition.—Larcoidea with quite irregular monothalamous shell, representing irregular modifications of an original lentelliptical latticed shell; the irregular cortical shell encloses a regular or subregular, lentelliptical or trizonal medullary shell.

The family Phorticida comprises a small number of Larcoidea in which a subregular, trizonal, lentelliptical medullary shell is enclosed by an irregular simple or spongy cortical shell. The lattice-work of the latter is sometimes simple and complete, at other times incomplete, with open gates (as in the Pylonida), sometimes also spongy. Its form is always more or less irregular, roundish, often dimply or tuberous; different from most other Larcoidea.

The medullary shell is constantly a regular or subregular Larnacilla-shell, composed of three elliptical latticed girdles of different sizes, perpendicular one to another. This leaves no doubt that the Phorticida are true Larcoidea. The connection of it with the cortical shell is rarely effected by radial beams, commonly by two opposite latticed wings, which are identical with the lateral halves of the transverse girdle in the Pylonida diplozonaria (Amphipyle, Tetrapyle). Often also between this transverse and a second (lateral) girdle there remain large open gates, so that the affinity between these Phorticida and the Pylonida cannot be doubted. In other cases these gates become closed, so that they more nearly approach the Larnacida. From both families they differ by the irregularity of the papillate or tuberous cortical shell. The network is more or less irregular, its surface often thorny, but never covered with symmetrically disposed radial spines.

The central capsule is lentelliptical, encloses the medullary shell, and is enveloped by the cortical shell, as in the nearly allied Pylonida and Larnacida, of which the Phorticida may be regarded as irregular aberrant forms.

Synopsis of the Genera of Phorticida.

Cortical shell simply latticed,	313. Phorticium.
Cortical shell spongy,	314. Spongophortis.

Genus 313. Phorticium,^[49] Haeckel, 1881, Prodromus, p. 464.

Definition.—Phorticida with irregular cortical shell of simple lattice-work, enclosing a lentelliptical Larnacilla-shaped medullary shell.

The genus Phorticium comprises all Phorticida in which the irregular cortical shell is formed by simple lattice-work, not by spongy framework. We can divide this genus into two subgenera: in Phortopyle (as in the Pylonida) the lattice-work of the cortical shell exhibits large openings or gates; in Phortolarcus these gates are perfectly closed by network; the former may be regarded as abnormal or irregular Pylonida, the latter as modifications of Larnacida.

Subgenus 1. Phortopyle, Haeckel.

Definition.—Lattice-work of the irregular cortical shell incomplete, with large openings or gates.

1. Phorticium pylonium, n. sp. (Pl. 49, fig. 10).

Cortical shell irregular, roundish, about three times as large as the enclosed lentelliptical, regular, Larnacilla-shell, connected with it by some radial beams and irregularly latticed girdles; between these remain four to eight large open gates of irregular roundish form and size; and these gates are the same as in Tetrapyle and Octopyle. This very variable species may be regarded as a monstrosity of those genera of Pylonida; it is very common, but all individuals are more or less unequal; some specimens approach to some common species of Tetrapyle. The surface of the shell is more or less spiny.

Dimensions.—Diameter of the irregular cortical shell 0.12 to 0.18; length of the lentelliptical medullary shell 0.05 to 0.06, breadth 0.035 to 0.045.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, &c., common, surface and in various depths.

2. Phorticium spironium, n. sp.

Cortical shell irregular, roundish, tuberous, about four times as large as the enclosed subregular Larnacilla-shell, connected with it by some irregular radial beams, and by opposite, spirally begining, irregularly latticed girdles, comparable to those of Spironium; between them remain six to twelve large open gates of irregular size and form. Surface rough. The resemblance to some forms of Spironium makes it probable that this species is a deformity or monstrosity of that genus.

Dimensions.—Diameter of the irregular cortical shell 0.12 to 0.2, of the lentelliptical medullary shell 0.03 to 0.06.

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

Subgenus 2. Phortolarcus, Haeckel.

Definition.—Lattice-work of the irregular cortical shell complete, without large openings or gates.

3. Phorticium deforme, n. sp.

Cortical shell irregular, roundish or longish, three times as large as the enclosed subregular, lentelliptical Larnacilla-shell, connected with it by two opposite latticed wings (the halves of the transverse girdle of Tetrapyle). Network of the cortical shell irregular, dense, perfectly closed, without larger openings or gates. Surface thorny. (May be regarded as a monstrous form of Larnacalpis.)

Dimensions.—Diameter of the irregular cortical shell 0.15 to 0.18, of the medullary shell 0.04 to 0.06.

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

4. Phorticium abnorme, n. sp.

Cortical shell irregular, roundish, tuberous, with five to ten quite irregular or nearly hemispherical protuberances, which resemble the cupolas of Zonarida. The regular lentelliptical Larnacilla-shell is one-third to one-fourth as large as the enclosing cortical shell, and is connected with it by some irregular radial beams. Lattice-work completely closed, without gates. Surface spiny. (May be regarded as an anomalous form of Zonidium; as in the other species of this variable genus, the individuals are very unequal.)

Dimensions.—Diameter of the irregular cortical shell 0.12 to 0.2, of the medullary shell 0.03 to 0.05.

Habitat.—Atlantic and Pacific, tropical zone, surface, and at various depths.

Genus 314. Spongophortis,^[50] Haeckel, 1881, Prodromus, p. 464.

Definition.—Phorticida with irregular cortical shell of spongy framework, enclosing a lentelliptical Larnacilla-shaped medullary shell.

The genus Spongophortis differs from Phorticium in the spongy framework of the cortical shell. This encloses the inner Larnacilla-shaped medullary shell either directly, or both shells are separated by a hollow interval, and connected either by radial beams or by latticed lamellæ. Perhaps both these subgenera might be better separated as genera.

Subgenus 1. Stypophorticium, Haeckel.

Definition.—Spongy cortical shell immediately enclosing the lentelliptical medullary shell, without hollow interval.

1. Spongophortis spongiosa, n. sp.

Cortical shell irregular, roundish, rough or tuberous, composed of loose spongy framework, which immediately envelops the lentelliptical central Larnacilla-shell; the diameter of the former becomes about five to six times as large as that of the latter.

Dimensions.—Diameter of the spongy cortical shell 0.15 to 0.25, of the trizonal medullary shell 0.03 to 0.04.

Habitat.—Pacific, central area, Station 274, surface.

Subgenus 2. Spongophorticium, Haeckel.

Definition.—Spongy cortical shell separated by a hollow interval from the lentelliptical medullary shell.

2. Spongophortis radiosa, n. sp.

Cortical shell irregular, roundish, four to five times as large as the enclosed lentelliptical Larnacilla-shell, with which it is connected by ten to twenty irregularly disposed radial beams. Spongy framework compact, about as thick as the medullary shell. Surface covered with numerous short, bristle-shaped, radial spines.

Dimensions.—Diameter of the spongy cortical shell 0.15 to 0.2, of the trizonal medullary shell 0.035 to 0.045.

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

3. Spongophortis larnacilla, n. sp. (Pl. 49, figs. 11a-11d).

Cortical shell irregular, roundish, tuberous, three to four times as large as the enclosed lentelliptical Larnacilla-shell, connected with it by two opposite latticed wings (the halves of the transverse girdle of Tetrapyle). Spongy framework compact, about half as thick as the medullary shell. Surface rough. (May be regarded as an abnormal Tetrapyle or Larnacalpis, with an irregular spongy cortical shell.)

Dimensions.—Diameter of the spongy cortical shell 0.16 to 0.2, of the trizonal medullary shell 0.04 to 0.06.

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

Family XXXII. Soreumida, Haeckel (Pl. 49, figs. 12, 13).

Soreumida, Haeckel, 1881, Prodromus, p. 464.

Definition.—Larcoidea with quite irregular polythalamous shell, composed of a variable number of chambers, aggregated without any definite order. Primordial chamber either simple or Larnacilla-shaped.

The family Soreumida contains a small number of Larcoidea, different from most other Sphærellaria in the complete irregularity of the polythalamous shell, which is composed of a variable number of roundish chambers or subspherical latticed shells, aggregated in the form of an irregular heap. We can distinguish in this family only two genera, with very different structure of the central medullary shell or the first chamber beginning the growth; and these correspond to the two subfamilies of the nearly allied Streblonida (p. 704). In Soreuma (as in Streblonia) the first or primordial chamber, from which the growth begins, is like the others, a simple spherical or irregular roundish lattice-shell. In Sorolarcus, however (as in Streblopyle), the first or primordial chamber is a trizonal or Larnacilla-shell. It is not improbable that the former originated phylogenetically from Streblonia, the latter from Streblopyle, by loss of the original spiral order of growth. But it is also possible that these groups have no nearer relation. Among the calcareous Foraminifera a very similar form is represented by Acervulina and its allies.

The general form of the whole shell in the Soreumida is sometimes more egg-shaped or lentelliptical, at other times even subspherical, occasionally quite irregular, tuberous, or clustered. The number of the aggregated chambers is very variable, in Sorolarcus between ten and thirty, in Soreuma ascending to fifty to eighty, sometimes from one hundred to one hundred and fifty and more. Their size is sometimes nearly equal, at other times very different, their form commonly very irregular, roundish, but sometimes also subspherical or egg-shaped. The network of the shell is also commonly irregular, with roundish pores of different sizes. The surface is usually smooth or rough, rarely covered with radial spines.

The central capsule is not known, as I observed only a few skeletons of this family.

Synopsis of the Genera of Soreumida.

Primordial chamber of the shell simple, subspherical or roundish,	315. Soreuma.
Primordial chamber of the shell trizonal or Larnacilla-shaped,	316. Sorolarcus.

Genus 315. Soreuma,^[51] Haeckel, 1881, Prodromus, p. 464.

Definition.—Soreumida with numerous chambers, aggregated without any regularity around one simple, spherical or subspherical, central chamber.

The genus Soreuma contains those Soreumida in which no trace of any regular structure is found, but all the chambers of the irregular shell are without any order, aggregated around a simple spherical or subspherical central chamber or medullary shell. Soreuma may have originated either from Sorolarcus by loss of the central Larnacilla-shell or from Cenolarcus by irregular apposition of new chambers around the lentelliptical central chamber or simple Larcoid-shell. Some species seem to exhibit a transition to Sorolarcus. Owing to the absolute irregularity of the polythalamous shell Soreuma resembles Acervulina among the Foraminifera.

Subgenus 1. Soreumium, Haeckel.

Definition.—Shell without radial spines.

1. Soreuma irregulare, n. sp. (Pl. 49, fig. 12).

Shell irregular, clustered, or tuberous, composed of a large number (one hundred and twenty to one hundred and fifty or more) of irregular, roundish chambers of very different sizes, the largest four to five times as broad as the smallest. Network very delicate, with very small roundish pores, to five times as broad as the bars. Surface thorny.

Dimensions.—Diameter of the shell 0.3, of the single chambers 0.02 to 0.08.

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

2. Soreuma acinosum, n. sp.

Shell irregularly lentelliptical, with different growth in the three dimensions, composed of a large number (forty to sixty or more) of irregular, roundish chambers of very different sizes, the largest six to eight times as broad as the smallest. Pores subregular, circular, twice as broad as the bars. Surface smooth.

Dimensions.—Length of the shell 0.21, breadth 0.17, height 0.13; diameter of the largest chambers 0.03, of the smallest 0.004.

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

3. Soreuma subglobosum, n. sp.

Shell nearly spherical, composed of a variable number (twelve to fifteen or more) of irregularly aggregated subspherical chambers of nearly equal size. Pores subregular, circular, twice as broad as the bars. Surface thorny.

Dimensions.—Diameter of the shell 0.25, of the largest chambers 0.04, of the smallest 0.005.

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

4. Soreuma acervulina, n. sp.

Shell quite irregular, cloddy, or tuberous, composed of twenty to thirty (or more) roundish chambers of almost uniform size, the largest twice to three times as broad as the smallest. Pores irregular, roundish. Surface smooth.

Dimensions.—Diameter of the shell 0.18 to 0.24, of the largest chambers 0.06, of the smallest 0.02.

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

Subgenus 2. Soreumidium, Haeckel.

Definition.—Shell with radial spines.

5. Soreuma spinosum, n. sp.

Shell quite irregular, cloddy, or tuberous, composed of thirty to forty subspherical chambers of nearly the same size. Pores subregular, circular, twice as broad as the bars; on the equator of each chamber six to eight pores. Surface thorny, covered with irregularly scattered conical radial spines, about as long as the diameter of the chambers.

Dimensions.—Diameter of the shell 0.17 to 0.25, of the chambers 0.04.

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

6. Soreuma setosum, n. sp.

Shell nearly spherical, composed of sixty to seventy (or more) irregular, roundish chambers of very different sizes, the largest five to six times as broad as the smallest. Pores irregular, roundish. Surface bristly, covered with very numerous, long and thin, bristle-shaped radial spines, about as long as the diameter of the shell.

Dimensions.—Diameter of the shell 0.28, of the chambers 0.005 to 0.03.

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

Genus 316. Sorolarcus,^[52] n. gen.

Definition.—Soreumida with numerous chambers, aggregated irregularly around a trizonal medullary shell or Larnacilla-shell.

The genus Sorolarcus comprises those Soreumida in which the heap of irregularly aggregated chambers encloses a central trizonal medullary shell, by which they demonstrate clearly their descent from Larnacida or Pylonida. The lentelliptical medullary shell exhibits quite the same characteristic structure as that of Larnacilla, being composed of three elliptical latticed girdles, perpendicular one to another. In some species also the beginning of a second system of girdles is clearly indicated, so that there can be no doubt as to their derivation from Amphipyle or Tetrapyle.

Subgenus 1. Sorolarcium, Haeckel.

Definition.—Shell without radial spines.

1. Sorolarcus larnacillifer, n. sp. (Pl. 49, fig. 13).

Shell irregular, clustered, or tuberous, composed of twenty to thirty irregular, roundish chambers of very different size, the largest four to eight times as broad as the smallest, aggregated without order around a central, lentelliptical, Larnacilla-shaped medullary shell. Pores irregular, roundish, twice to four times as broad as the bars. Surface smooth or a little spiny.

Dimensions.—Diameter of the whole shell 0.18, of the central Larnacilla-shell 0.05.

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

2. Sorolarcus tetrapylifer, n. sp.

Shell irregularly roundish, clustered, composed of ten to twelve irregular rather long chambers of almost uniform size, the largest twice as broad as the smallest, aggregated without order around a central shell of the structure of Tetrapyle, which encloses an inner trizonal Larnacilla-shell of half the size. Pores irregular, roundish, twice to four times as broad as the bars. Surface spiny.

Dimensions.—Diameter of the whole shell 0.25, of the outer (Tetrapyle-like) medullary shell 0.12, of the inner (Larnacilla-like) shell 0.06.

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

Subgenus 2. Sorolarcidium, Haeckel.

Definition.—Shell with radial spines.

3. Sorolarcus terminalis, n. sp.

Shell nearly spherical, composed of fifteen to eighteen irregularly aggregated roundish chambers of nearly equal size; in the centre a lentelliptical Larnacilla-shell. Surface covered with numerous thin, bristle-like radial spines, somewhat longer than the shell.

Dimensions.—Diameter of the whole shell 0.21, of the central Larnacilla-shell 0.05.

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

1. Cenolarcus = Hollow basket; κενός, λάρκος.
2. Larcarium = A kind of basket; λαρκάριον.
3. Coccolarcus = Basket with kernel; κόκκος, λάρκος.
4. Larcidium = Little basket, diminutive of Larcus; λαρκίδιον.
5. Spongolarcus = Spongy basket; σπόγγος, λάρκος.
6. Stypolarcus = Hemp basket; στύπη, λάρκος.
7. Larnacilla = Little chest, diminutive of Larnax; λάρναξ.
8. Larnacidium = Little chest, diminutive of Larnax; λάρναξ.
9. Larnacalpis = Tankard-shaped chest; λάρναξ, κάλπις.
10. Larnacantha = Chest with spines; λάρναξ, ἄκανθα.
11. Larnacoma = Shell of chest form; λάρναξ.
12. Larnacospongus = Spongy chest; λάρναξ, σπόγγος.
13. Larnacostupa = Chest with hemp envelop; λάρναξ, στύπη.
14. Monozonium = With one girdle; μονοζωνίον.
15. Dizonium = With two girdles; διζωνίον.
16. Trizonium = With three girdles; τριζωνίον.
17. Amphipyle = With one gate on both sides; ἀμφί, πύλη.
18. Tetrapyle = With four gate-openings; τετραπύλη.
19. Octopyle = With eight gate-openings; ὀκτώ, πύλη.
20. Pylonium = Building with gates; πυλώνιον.
21. Amphipylonium = With one large gate on either side; ἀμφί, πυλώνιον.
22. Tetrapylonium = Building with four gates; τέτρα, πυλώνιον.
23. Pylozonium = Shell with gates and girdles; πύλη, ζωνίον.
24. Tholartus = Cupola-bread; θόλος, ἄρτος.
25. Tholodes = Cupola-shaped; θολώδης vel θολοειδής.
26. Amphitholus = Shell with two opposite cupolas; ἀμφί, θόλος.
27. Amphitholonium = Small shell with two opposite cupolas; ἀμφί, θολώνιον.
28. Tholostaurus = Cross of four cupolas; θόλος, σταυρός.
29. Tholoma = Dome-building; θολῶμα.
30. Alternating, μεταλλάσσων.
31. Staurotholus = Cupolas cross-wise disposed; σταυρός, θόλος.
32. Staurotholonium = Small shell with cupolas cross-wise disposed; σταυρός, θολώνιον.
33. Tholocubus = Cube with six cupolas on its sides; θόλος, κῦβος.
34. Tholonium = Shell with cupolas; θολώνιον.
35. Cubotholus = Shell with cupolas disposed on six cube-sides; κῦβος, θόλος.
36. Cubotholonium = Small shell with cupolas disposed on the six sides of a cube; κῦβος, θολώνιον.
37. Zonarium = Small girdle; ζωνάριον.
38. Zoniscus = Elegant girdle; ζωνίσκος.
39. Zonidium = Little girdle; ζωνίδιον.
40. Spirema = Convolution, turning; σπείρημα.
41. Lithelius = Stony sun; λίθος, ἥλιος.
42. Larcospira = Spiral basket; λάρκος, σπεῖρα.
43. Pylospira = Spiral shell with internal gates; πύλη, σπεῖρα.
44. Tholospira = Shell with spiral domes; θόλος, σπεῖρα.
45. Spironium = Shell with spiral structure; σπειρώνιον.
46. Streblonia = Screw-shell; στρεβλώνιον.
47. Streblacantha = Screw-shell with spines; στρέβλη, ἄκανθα.
48. Streblopyle = Screw-shell with gates; στρέβλη, πύλη.
49. Phorticium = Small vessel; φορτικίον.
50. Spongophortis = Spongy vessel; σπόγγος, φορτίς.
51. Soreuma = σώρευμα, heap.
52. Sorolarcus = Basket heap; σωρός, λάρκος.