1. Pylolena inermis, n. sp.

Arms club-shaped, at the base half as broad, at the rounded distal end as broad as the triopyle-shaped medullary shell. Surface and margin smooth.

Dimensions.—Diameter of the cortical shell 0.15, of the medullary shell 0.05.

Habitat.—Equatorial Atlantic, Station 347, surface; Central Pacific, Station 272, surface.

2. Pylolena armata, n. sp. (Pl. 48, fig. 15).

Arms trapezoid, at the base half as broad, at the distal end twice as broad as the triopyle-shaped medullary shell. Surface and margin thorny. Twelve strong conical spines at the distal end of the three arms, two opposite on both faces of the arm-edges.

Dimensions.—Diameter of the cortical shell 0.2, of the medullary shell 0.06.

Habitat.—South Atlantic, Station 325, surface.

Genus 249. Hexapyle,^[288] Haeckel, 1881, Prodromus, p. 464.

Definition.—Pylodiscida with triopyle-shaped medullary shell, surrounded by three distal arm-chambers. Notches between the three arms transformed into gates by a connecting equatorial girdle.

The genus Hexapyle differs from the preceding Pylolene in the development of an equatorial ring or latticed girdle, which connects the free extremities of the three distal ends and transforms the open notches between them into gates. It simulates therefore the formation of Triopyle, from which it differs by duplication of the arm-joints and of the gates (in each radius occur one proximal and one distal gate).

1. Hexapyle triangula, n. sp.

Cortical shell triangular, with three rounded corners, three times as broad as the triangular triopyle-shaped medullary shell. Surface smooth or rough, but not spiny. Three arms two-thirds as broad as the three egg-shaped gates of each side.

Dimensions.—Diameter of the cortical shell (or length of one side of the triangle) 0.15, of the medullary shell 0.05; breadth of the gates 0.06, of the bridges between them 0.04.

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

2. Hexapyle sexangula, n. sp.

Cortical shell hexagonal, with six equal sides, four times as broad as the triangular triopyle-shaped medullary shell. Surface rough, but not spiny. Three arms (on their smallest part) half as broad as the three triangular gates (on their broadest part).

Dimensions.—Diameter of the cortical shell 0.16, of the medullary shell 0.04; breadth of the gates 0.06, of the bridges 0.03.

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

3. Hexapyle circularis, n. sp.

Cortical shell circular, four times as broad as the triangular, Triopyle-shaped medullary shell. Surface smooth. Three arms half as broad as the three kidney-shaped gates on each side of the shell.

Dimensions.—Diameter of the cortical shell 0.2, of the medullary shell 0.05; breadth of the gates 0.08, of the bridges between them 0.04.

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

4. Hexapyle triacantha, n. sp.

Cortical shell triangular, thorny, with three pointed corners, prolonged into three strong conical radial spines; its diameter four times as great as that of the medullary shell. Three arms of the same breadth as the three egg-shaped gates of each side.

Dimensions.—Diameter of the cortical shell (or length of one side of the triangle, without spines) 0.2, of the medullary shell 0.05; breadth of the gates and of the bridges between them 0.06.

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

5. Hexapyle hexacantha, n. sp.

Cortical shell hexagonal, thorny, three times as broad as the medullary shell. Six stronger conical radial spines on the six corners at equal distances, lying in the equatorial plane of the disk. Three half girdles half as broad as the three triangular gates of each side.

Dimensions.—Diameter of the cortical shell 0.15, of the medullary shell 0.05; breadth of the gates 0.05, of the bridges 0.025.

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

6. Hexapyle dodecantha, n. sp. (Pl. 48, fig. 16).

Cortical shell triangular, thorny, with rounded corners, three and a half times as broad as the medullary shell. Twelve stronger radial spines, six opposite in pairs on each side of the discoidal shell, as prolongations of the lateral edges of the triangular gates, which are about the same breadth as the half girdles between them.

Dimensions.—Diameter of the cortical shell 0.21, of the medullary shell 0.06; breadth of the gates and of the bridges 0.06.

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

7. Hexapyle polyacantha, n. sp.

Cortical shell circular, thorny, with a circle of numerous conical radial spines in the periphery; its diameter nearly three times as great as that of the medullary shell. Three half-girdles half as broad as the three kidney-shaped gates on each side of the discoidal shell.

Dimensions.—Diameter of the cortical shell 0.11, of the medullary shell 0.04; breadth of the gates 0.04, of the bridges between them 0.02.

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

Genus 250. Pylodiscus,^[289] n. gen.

Definition.—Pylodiscida with Triopyle-shaped medullary shell, surrounded by three distal arm-chambers. Notches between the three arms closed by lattice-work and by an equatorial girdle.

The genus Pylodiscus differs from Hexapyle in the development of two convex plates of lattice-work, which close the six open gates and transform the disk into a biconvex fenestrated lens. Pylodiscus simulates therefore the characteristic form of Triodiscus; but whilst in the latter we find only three arm-joints and three simple gates, their number is doubled in the former.

1. Pylodiscus triangularis, n. sp. (Pl. 48, fig. 17).

Cortical shell triangular, with rounded corners, three times as broad as the triangular, Triopyle-shaped medullary shell. Three arms about as broad as the three egg-shaped gates between them. (Differs from Hexapyle triangula only by the delicate network of both triangular convex covering plates, which close the open gates.) Six larger and many smaller spines on the margin of the disk.

Dimensions.—Diameter of the disk 0.15, of the gates 0.05.

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

2. Pylodiscus sexangularis, n. sp.

Cortical shell hexangular, equilateral, four times as broad as the circular, Triopyle-shaped medullary shell. Surface spiny. Three arms nearly of the same form and size as the three triangular gates between them. (Similar to Hexapyle sexangularis, but differing in the irregular loose network closing the gates.)

Dimensions.—Diameter of the disk 0.18, of the gates 0.06.

Habitat.—North Pacific, south of Japan, Station 237, surface

3. Pylodiscus cardiopylus, n. sp.

Cortical shell hexangular, equilateral, five times as broad as the triangular, Triopyle-shaped medullary shell. Surface smooth. Three arms triangular, at the distal end as broad as the three heart-shaped gates. On the margin six strong pyramidal spines in the equatorial plane (adradial, as prolongations of the lateral arm-edges).

Dimensions.—Diameter of the disk 0.15, of the gates 0.05.

Habitat.—Indian Ocean, Sunda Strait, Rabbe.

4. Pylodiscus nephropylus, n. sp.

Cortical shell circular, three times as broad as the circular, Triopyle-shaped medullary shell. Surface spiny. Three arms trapezoidal, half as broad as the three kidney-shaped gates. On the margin twelve stronger, conical, radial spines, opposite in pairs on both sides of the disk, disposed in six pairs at the distal end of the arms.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.06.

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

Subfamily 3. Discopylida, Haeckel.

Definition.—Pylodiscida with Triopyle-shaped medullary shell and Pylodiscus-shaped cortical shell, which is surrounded by a marginal chambered equatorial girdle.

Genus 251. Discozonium,^[290] n. gen.

Definition.—Pylodiscida with Triopyle-shaped medullary shell and Pylodiscus-shaped cortical shell, which is surrounded by an equatorial chambered girdle. No peculiar osculum on the margin of the disk.

The genus Discozonium and the following Discopyle make up together the small group of the Discopylida, or those Pylodiscida in which a discoidal shell like Pylodiscus is surrounded by a marginal equatorial girdle; this girdle is divided into twelve to twenty-four or more chambers by radial beams, which are the external prolongations of the radial marginal spines of Pylodiscus. The latter genus bears therefore to Discozonium the same relation as Sethodiscus in the other Discoidea does to Lithocyclia, or Phacodiscus to Coccodiscus.

1. Discozonium cyclonium, n. sp.

Disk circular, lenticular, with smooth margin, three times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell kidney-shaped, twice as broad as the three arms. Chambered equatorial girdle with twenty to twenty-four subregular chambers (similar to Discopyle osculata, Pl. 48, fig. 19, but without any marginal osculum).

Dimensions.—Diameter of the disk 0.2, of the cortical shell 0.14, of the medullary shell 0.07.

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

2. Discozonium trigonium, n. sp.

Disk triangular, with thorny margin, four times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell egg-shaped, scarcely as broad as the three arms. Chambered equatorial girdle with twenty-four to thirty irregular chambers.

Dimensions.—Diameter of the disk 0.24, of the cortical shell 0.2, of the medullary shell 0.06.

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

3. Discozonium hexagonium, n. sp. (Pl. 48, fig. 18).

Disk hexagonal, with spiny margin, four times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell kidney-shaped, one and a half times as broad as the arms. Chambered equatorial girdle with twelve large regular chambers; the radial beams between them are prolonged into twelve strong pyramidal marginal spines (three perradial on the ends of the arms, three interradial on the radii of the gates, six adradial between the former and latter).

Dimensions.—Diameter of the disk 0.2, of the cortical shell 0.12, of the medullary shell 0.05.

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

Genus 252. Discopyle,^[291] n. gen.

Definition.—Pylodiscida with Triopyle-shaped medullary shell and Pylodiscus-shaped cortical shell, which is surrounded by an equatorial chambered girdle. One peculiar osculum, surrounded by a corona of spines, on the margin of the disk.

The genus Discopyle differs from the preceding genus Discozonium in the development of a peculiar marginal osculum, and bears therefore to it the same relation as, in the Porodiscida, Ommatodiscus does to Porodiscus (compare above, p. 500). This peculiar osculum is here also surrounded by a corona of spines, and serves probably for the exit or outlet of a bunch of pseudopodia or a "sarcode-flagellum." Only two species of Discopyle have been observed, which represent perhaps better two different genera; in one species the disk is circular, in the other elliptical. In this latter the osculum lies on one pole of the main axis.

1. Discopyle osculata, n. sp. (Pl. 48, fig. 19).

Disk circular with spiny margin, three times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell kidney-shaped, on the inside with an interradial spine, twice as broad as the three pentagonal arms. Chambered equatorial girdle with twenty-four subregular chambers, in the radius of one odd gate with a large marginal osculum, which is as broad as the medullary shell, and surrounded by a dense corona of twenty to thirty strong conical spines.

Dimensions.—Diameter of the disk 0.15, of the cortical shell 0.1, of the medullary shell 0.05, of the marginal osculum 0.06.

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

2. Discopyle elliptica, n. sp. (Pl. 48, fig. 20).

Disk elliptical, four-fifths as broad as long, with spiny margin, three times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell roundish, on the inside with an interradial spine, little broader than the quadrangular arms. Chambered equatorial girdle with twenty to thirty irregular chambers, on one pole of the main axis with a large marginal osculum, which is one-third as broad as the length of the main axis, and armed with a corona of twenty to thirty short conical spines. The osculum does not correspond to a certain radius.

Dimensions.—Diameter of the disk 0.15, of the cortical shell 0.08, of the medullary shell 0.04, of the marginal osculum 0.05.

Habitat.—Central Pacific, Station 267, depth 2700 fathoms.

Family XXIII. Spongodiscida, Haeckel (Pl. 41, fig. 11).

Definition.—Discoidea without a phacoid shell, with a flat discoidal shell, in which a simple spherical central chamber is surrounded by an irregular spongy framework (sometimes with concentric rings around the central chamber). Surface of the disk quite spongy, without porous sieve-plates.

The family Spongodiscida is the sixth and last family of the Discoidea, and bears to the other families of this group the same relation as the family Spongosphærida does to the other Sphæroidea, or the Spongurida to the other Prunoidea. Its characteristic structure consists in the irregular spongy framework of the disk, and mainly in the rough, irregular shape of its spongy surface, which is never covered with porous plates (neither phacoid shell nor corresponding sieve-plates), as in all other Discoidea. Of course a little spongy structure occurs also in many Porodiscida and even in some Coccodiscida (principally in the peripheral part of the disk or its chambered arms); but both flat (or convex) surfaces of the disk (at least in the central part) remain here constantly as simple lattice-plates, whilst in all Spongodiscida the whole surface of the disk is spongy.

When I constituted the family Spongodiscida in my Monograph (1862, pp. 452, 460) I had separated from them the Spongocyclida, exhibiting in the central part of the disk a more or less distinct concentric arrangement of the spongy chambers, whilst in the former the delicate spongy framework is quite irregular, composed of branched siliceous threads, connected and interwoven in all directions. But in all Spongocyclida the whole surface of the spongy disk is quite as irregularly rough and deprived of smooth sieve-plates as in all true Spongodiscida, and the more or less concentric structure of the central part of the disk in the former (very variable and often scarcely able to be recognised) seems not sufficient to separate both groups; even the single genera cannot be sufficiently separated by this character. I now therefore give up entirely the group of Spongocyclida (as already done in my Prodromus, 1881). Nevertheless the concentric annular structure in the dark central part of some Spongodiscida is very interesting as transition to the Porodiscida; it indicates already that the former are derived from the latter. Even the single genera in both families are corresponding.

In the new system of "Polycystina," which Ehrenberg gave, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, p. 157), are enumerated under the Calodictya four genera "with spongy disk," viz., Spongodiscus, Rhopalodictyum, Dictyocoryne, Spongaster. Indeed these four genera, which I here retain, are true Spongodiscida, and must be separated from the other Calodictya, the greater part of which are Porodiscida. The number of species of true Spongodiscida now amounts to sixty-seven, which I dispose in thirteen genera.

The whole family may be divided into three subfamilies. The first of these are the Spongophacida (corresponding to the Trematodiscida among the Porodiscida), in which the circular margin of the spongy disk bears no radial appendages; either the margin is quite simple, spongy (Spongodiscus), or surrounded by a hyaline, solid, or porous equatorial girdle (Spongophacus). The disk is either more lenticular (biconvex) or more flat discoidal (a shortened cylinder), rarely a little biconcave (thicker at the margin than in the centre). The spongy framework of the solid disk is either quite irregular (Spongodisculus), or in the central part with concentric circular rings (Spongocyclia), or in the central part spirally convoluted (Spongospira).

The second subfamily, Spongotrochida, corresponds to the Stylodictyida (among the Porodiscida), and is distinguished by solid radial spines on the margin of the disk, disposed in the equatorial plane either irregularly or regularly (after the same order as in the other families of Discoidea).

The third subfamily, Spongobrachida, correspond perfectly to the Euchitonida (among the Porodiscida), bearing on the disk-margin two, three, or four spongy arms, commonly disposed regularly in the equatorial plane. Here also occurs the peculiar formation of a "patagium," or of an interbrachial spongy framework different from that of the arms, which connects the arms like a web-membrane in the equatorial plane.

The spongy framework exhibits in all these Spongodiscida no remarkable differences, being everywhere composed of fine branched solid siliceous threads, interwoven in all directions, with irregular meshes of very different size.

The central capsule of all Spongodiscida is filled up with the same spongy framework which covers also both its sides. It grows according to the enveloping skeleton, but remains constantly smaller. The form of the central capsule is circular (lenticular or discoidal) in the Spongophacida and Spongotrochida, whilst in the Spongobrachida it enters into the radial spongy arms, developed from the margin of the spongy disk.

Synopsis of the Genera of the Spongodiscida.

Subfamily 1. Spongophacida, Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with a simple circular disk, without radial appendages on the margin (neither solid spines nor chambered arms).

Genus 253. Spongodiscus,^[292] Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 237.

Definition.—Spongodiscida with a simple circular disk, without radial appendages and without an equatorial girdle on the margin.

The genus Spongodiscus represents the most simple and primitive form of the Spongodiscida, or of those Discoidea in which the central disk is more or less spongy, composed of an irregular fine framework. In my Monograph (1862, pp. 452, 460, 469) I had separated the true Spongodiscus (first described by Ehrenberg, loc. cit.) and the Spongocyclia; the former being characterised by the irregular spongy framework of the whole disk, whilst in the latter this framework includes in the central part some concentric circular rings (approaching Porodiscus). In the same way afterwards Stöhr (1880, loc. cit.) separated the genus Spongospira as spongy disks, which include in the central part some spiral convolutions. But as these differences are rather inconstant and not sharply discernible, I think it now better to regard these three forms as subgenera of Spongodiscus. All three have the common simple circular disk, without any marginal appendages.

Subgenus 1. Spongodisculus, Haeckel.

Definition.—Spongy framework of the disk quite irregular, without concentric rings or spiral convolutions.

1. Spongodiscus mediterraneus, Haeckel.

Spongy disk plain on both sides, with quite an irregular framework, without concentric rings and without radial piercing beams. Texture everywhere uniform; meshes eight to ten times as broad as the bars.

Dimensions.—Diameter of the disk 0.08 to 0.24, of the meshes 0.005 to 0.008.

Habitat.—Mediterranean (Messina), Haeckel; also fossil in the Tertiary rocks of Sicily (Grotte), Stöhr.

2. Spongodiscus radiatus, n. sp.

Spongy disk plain on both sides, with quite irregular framework, without concentric rings, but with numerous piercing radial beams which are not prolonged into marginal spines. Texture everywhere uniform; meshes once and a half to twice as broad as the bars.

Dimensions.—Diameter of the disk 0.12 to 0.15, of the meshes 0.002 to 0.003.

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

3. Spongodiscus resurgens, Ehrenberg.

Spongy disk lenticular, biconvex, in the darker centre much thicker than towards the thin periphery, with an irregular framework, without concentric rings, but with numerous piercing radial beams. Texture equal; meshes three to four times as broad as the bars.

Dimensions.—Diameter of the disk 0.1 to 0.3, of the meshes 0.003 to 0.006.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in the Tertiary rocks of Sicily and Barbados.

4. Spongodiscus favus, Ehrenberg.

Spongy disk lenticular, biconvex, in the darker centre much thicker than towards the periphery, with an irregular framework, without concentric rings. Texture different, in the outer half with numerous radial beams and loose network, the meshes of which are three to four times as large as in the darker and denser framework of the centre.

Dimensions.—Diameter of the disk 0.2, of the outer meshes 0.008 to 0.012, of the inner meshes 0.002 to 0.003.

Habitat.—North Atlantic, Greenland, Færöe Channel (John Murray), surface.

5. Spongodiscus biconcavus, n. sp.

Spongy disk biconcave, in the peripheral, ring-like, thickened part twice as thick as in the hollowed central part, with an irregular framework, without concentric rings. Texture different, in the outer half looser than in the inner, darker part; meshes of the outer part five to six times, of the inner twice to three times, as broad as the bars.

Dimensions.—Diameter of the disk 0.25, of the outer meshes 0.01 to 0.012, of the inner 0.004 to 0.006.

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

Subgenus 2. Spongocyclia, Haeckel, 1862, Monogr. d. Radiol., p. 469.

Definition.—Spongy framework of the disk in the inner part with concentric, circular rings, in the outer part irregular.

6. Spongodiscus cycloides, Haeckel.

Spongy disk on both sides plain, in the central part with five to ten concentric, circular rings, in the peripheral part quite irregularly and densely spongy. Meshes twice to four times as broad as the bars.

Dimensions.—Diameter of the disk 0.1 to 0.2, of the meshes 0.003 to 0.006.

Habitat.—Mediterranean (Messina), North Atlantic (Canary Islands).

7. Spongodiscus spongocyclia, Haeckel.

Spongy disk lenticular, in the thicker central part with eleven to twelve circular, concentric rings, in the thinner, peripheral zone irregularly spongy. Meshes twice to four times as broad as the bars. (The triangular form in the specimen figured by Stöhr is accidental, produced by the broken margin.)

Dimensions.—Diameter of the disk 0.2 to 0.3, of the meshes 0.006 to 0.008.

Habitat.—Fossil in Tertiary rocks of Barbados (Haeckel) and Sicily (Stöhr).

Subgenus 3. Spongospira, Stöhr, 1880, Palæontogr., vol xxvi. p. 120.

Definition.—Spongy framework of the disk in the inner part with spiral convolutions, in the outer part irregular.

8. Spongodiscus florealis, Haeckel.

Spongy disk lenticular, in the thicker central part with five to six spiral convolutions, in the outer peripheral zone irregularly spongy. No radial beams piercing the framework. Meshes three to four times as broad as the bars.

Dimensions.—Diameter of the disk 0.26, of the meshes 0.006 to 0.008.

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

9. Spongodiscus spiralis, n. sp.

Spongy disk on both sides plain, with twelve to sixteen spiral convolutions in the central part, with irregular, spongy framework in the outer part, pierced by numerous interrupted radial beams. Meshes five to six times as broad as the bars.

Dimensions.—Diameter of the disk 0.2 to 0.3, of the meshes 0.01 to 0.012.

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

Genus 254. Spongophacus,^[293] Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with a simple circular disk, without radial appendages, on the margin surrounded by a thin porous or solid equatorial girdle.

The genus Spongophacus, represented hitherto only by a single but interesting species, differs from Spongodiscus by the peculiar girdle which surrounds the margin of the disk in the equatorial plane. It simulates the same formation as Perichlamydium in the Porodiscida, and resembles also Periphæna, &c., in the Phacodiscida.

1. Spongophacus periphæna, n. sp.

Spongy disk lenticular, with an irregular, dense framework, in the centre darker than in the peripheral part. Margin of the disk very thin, surrounded by a broad, circular girdle, lying in the equatorial plane, about as broad as the half radius of the spongy disk. The inner part of the girdle is perforated by numerous irregular, small pores, which pass over gradually into the spongy meshes; the outer part is quite homogeneous, solid, transparent, with an extremely thin margin.

Dimensions.—Diameter of the disk 0.2; breadth of the girdle 0.05.

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

Subfamily 2. Spongotrochida, Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with a circular disk, the margin of which is armed with solid radial spines, situated in the equatorial plane (rarely also on both sides of the disk with radial spines).

Genus 255. Spongolonche,^[294] Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with two solid marginal spines, opposite in one equatorial diameter of the disk.

The genus Spongolonche opens the series of the Spongotrochida, or of those Spongodiscida in which the margin of the disk is armed with solid radial spines, situated in the equatorial plane. Spongolonche possesses only two such spines, opposite in one equatorial diameter of the disk; it corresponds therefore to Stylocyclia among the Coccodiscida, to Xiphodictya among the Porodiscida.