Subfamily 2. Trochodiscida, Haeckel

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

Genus 177. Stylodiscus, n. gen.

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

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

Subgenus 1. Stylentodiscus, Haeckel.

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

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

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

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

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

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

Subgenus 2. Stylexodiscus, Haeckel.

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

2. Stylodiscus amphistylus, n. sp.

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

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

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

Genus 178. Theodiscus, n. gen.

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

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

Subgenus 1. Theodiscoma, Haeckel.

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

1. Theodiscus divinus, n. sp.

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

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

Habitat.—Central Pacific, Station 265, surface.

2. Theodiscus christianus, n. sp.

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

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

Habitat.—Central Pacific, Station 271, surface.

3. Theodiscus trinitatis, n. sp.

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

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

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

Subgenus 2. Theodiscura, Haeckel.

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

4. Theodiscus vanitatis, n. sp.

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

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

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

5. Theodiscus nirvana, n. sp.

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

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

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

Genus 179. Crucidiscus, n. gen.

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

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

Subgenus 1. Staurentodiscus, Haeckel.

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

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

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

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

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

Subgenus 2. Staurexodiscus, Haeckel.

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

2. Crucidiscus cuspidatus, n. sp.

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

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

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

3. Crucidiscus echinatus, n. sp.

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

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

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

4. Crucidiscus cruciatus, n. sp.

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

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

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

Genus 180. Trochodiscus, n. gen.

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

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

Subgenus 1. Trochodisculus, Haeckel.

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

1. Trochodiscus cenophacus, n. sp.

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

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

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

2. Trochodiscus medusinus, n. sp.

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

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

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

3. Trochodiscus odontotrochus, n. sp.

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

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

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

4. Trochodiscus solaris, n. sp.

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

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

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

5. Trochodiscus echiniscus, n. sp.

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

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

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

Subgenus 2. Pristodiscus, Haeckel.

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

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

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

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

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

7. Trochodiscus cingillum, n. sp.

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

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

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