Legion I. SPUMELLARIA, (continued 16)

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. 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. Cortical shell only with one perfect (transverse) girdle, 282. Amphipyle.

Cortical shell with two perfect girdles (the transverse and lateral). 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. 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.

I. Subfamily Haplozonaria. One system of girdles. Medullary shell simple, spherical or lentelliptical; cortical shell simple, with one, two, or three girdles.

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.

II. Subfamily Diplozonaria. Two systems of concentric girdles. Medullary shell trizonal, with three perfect girdles; cortical shell simple, with one, two or three girdles.

Cortical shell only with one perfect (transverse) girdle,

282. Amphipyle.

Cortical shell with two perfect girdles (the transverse and lateral).

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.

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,^[318] 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.

Monozonium hartingii = Haliomma amphiaspis, Harting, 1863 (L. N. 18, p. 15, pl. 2, fig. 43).

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,^[319] 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,^[320] 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,^[321] 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,^[322] 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,^[323] 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,^[324] 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,^[325] 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,^[326] 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,^[327] 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.) Central chamber simple, without medullary shell. Two simple cupolas (without veil), 289. Tholartus.

Two double cupolas (with veil), 290. Tholodes.

Central chamber Larnacilla-shaped, with enclosed medullary shell. 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.) Central chamber simple, without medullary shell. Four simple cupolas (without veil), 293. Tholostaurus.

Four double cupolas (with veil), 294. Tholoma.

Central chamber Larnacilla-shaped, with enclosed medullary shell. 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.) Central chamber simple, without medullary shell. Six simple cupolas (without veil), 297. Tholocubus.

Six double cupolas (with veil), 298. Tholonium.

Central chamber Larnacilla-shaped, with enclosed medullary shell. Six simple cupolas (without veil, 299. Cubotholus.

Six double cupolas (with veil), 300. Cubotholonium.

I. Subfamily Amphitholida. Cupolas developed only in the direction of one single axis (commonly two cupolas). (Tholonida unidimensiva.)

Central chamber simple, without medullary shell.

Two simple cupolas (without veil),

289. Tholartus.

Two double cupolas (with veil),

290. Tholodes.

Central chamber Larnacilla-shaped, with enclosed medullary shell.

Two simple cupolas (without veil),

291. Amphitholus.

Two double cupolas (with veil),

292. Amphitholonium.

II. Subfamily Staurotholida. Cupolas developed in the direction of two axes perpendicular one to another (commonly four cupolas). (Tholonida bidimensiva.)

Central chamber simple, without medullary shell.

Four simple cupolas (without veil),

293. Tholostaurus.

Four double cupolas (with veil),

294. Tholoma.

Central chamber Larnacilla-shaped, with enclosed medullary shell.

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.)

Central chamber simple, without medullary shell.

Six simple cupolas (without veil),

297. Tholocubus.

Six double cupolas (with veil),

298. Tholonium.

Central chamber Larnacilla-shaped, with enclosed medullary shell.

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,^[328] 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,^[329] 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,^[330] 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,^[331] 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,^[332] 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,^[333] 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.