Subfamily 3. Heliodiscida, Haeckel, 1881, Prodromus, p. 457

Definition.—Phacodiscida with a variable number of radial spines on the margin of the disk (ten to twenty or more), which are commonly more or less irregular (sometimes regularly formed and disposed).

Genus 193. Heliodiscus, Haeckel, 1862, Monogr. d. Radiol., p. 436.

Definition.—Phacodiscida with simple medullary shell and with numerous (ten to twenty or more) simple radial spines on the margin of the disk (commonly with a variable number and an irregular disposition of the undivided spines).

The genus Heliodiscus, the most common and polymorphic of all Phacodiscida, was founded by me in 1862 as the first known type of this family (loc. cit.). I use here the diagnosis of this genus in a restricted sense, including only the species, in which the number of marginal spines amounts to ten, twenty, or more (sometimes fifty to eighty, rarely more than one hundred). The number of spines is in the different species variable, and their disposition commonly more or less irregular, whilst in the preceding genera (with two, three, four, six, or eight marginal spines) their distance and form are commonly regular.

Subgenus 1. Heliodiscetta, Haeckel.

Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

1. Heliodiscus asteriscus, n. sp. (Pl. , fig. 8).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; ten to twelve on the radius of the disk. Marginal spines fifteen to twenty, conical, often double contoured, of variable size and disposition, the largest as long as the radius of the disk, as broad at the base as one pore.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the radial spines 0.04 to 0.07, basal breadth 0.01.

Habitat.—Cosmopolitan; Mediterranean (Corfu), Indian Ocean (Madagascar), Atlantic and Pacific, many Stations, surface and various depths.

2. Heliodiscus trochiscus, n. sp. (Pl. , figs. 10, 13).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; fourteen to sixteen on the radius. Marginal spines twelve to sixteen, conical, of variable size and disposition, the largest as long as the diameter of the medullary shell, twice as broad as one pore.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.01 to 0.025, basal breadth 0.005.

Habitat.—Central Pacific, Stations 272 to 274, surface.

3. Heliodiscus trigonodon, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; eighteen to twenty on the radius. Marginal spines sixteen to twenty, equilateral triangular, flat, smooth, about as long and broad as the radius of the medullary shell.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.03, basal breadth 0.03.

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

4. Heliodiscus glyphodon, n. sp. (Pl. , fig. 2).

Heliosestrum glyphodon, Haeckel, 1881, Prodromus et Atlas (pl. xxxv. fig. 2).

Disk with smooth surface, four times as broad as the medullary shell. Pores subregular, circular; seven to eight on the radius. Marginal spines ten to twelve, equilateral triangular, flat, deeply furrowed, twice as long as broad, and as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.14, of the medullary shell 0.035; length of the radial spines 0.07, basal breadth 0.035.

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

5. Heliodiscus helianthus, Haeckel.

Haliomma helianthus, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. fig. 1.

Disk with smooth surface, five times as broad as the medullary shell. Pores regular, oblong, disposed regularly in sixty to eighty radial series; fourteen to sixteen on the radius. Marginal spines sixty to eighty, conical, about as long as the diameter of the medullary shell, twice as broad as one pore.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.04; length of the radial spines 0.04, basal breadth 0.005.

Habitat.—Fossil in Barbados.

6. Heliodiscus sol, Haeckel.

Haliomma sol, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 52.

Heliodiscus sol, Haeckel, 1862, Monogr. d. Radiol., p. 438.

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; eight to ten on the radius. Marginal spines twenty to thirty, conical, the largest as long as the radius of the medullary shell, their bases widely distant. (The species from Barbados figured by Ehrenberg, 1875, as Haliomma sol, appertains to Heliosestrum solare.)

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.02 to 0.025, basal breadth 0.01.

Habitat.—Fossil in Tertiary rocks of Greece (Ægina), Ehrenberg.

7 Heliodiscus siculus, Stöhr.

Heliodiscus siculus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 89, Taf. i. fig. 14.

Disk with smooth surface, three times as broad as the medullary shell. Pores irregular roundish; seven to eight on the radius. Marginal spines forty to fifty, conical, very irregular, the largest as long as the radius of the medullary shell, their bases coming in contact.

Dimensions.—Diameter of the disk 0.13 to 0.15, of the medullary shell 0.04 to 0.05; length of the radial spines 0.02 to 0.03, basal breadth 0.002 to 0.006.

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

8. Heliodiscus polymorphus, n. sp. (Pl. , figs. 11, 12).

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius. Marginal spines ten to fifteen, pyramidal, angular, very irregular and variable in size and distribution, the largest nearly as long as the diameter of the disk, as broad at the base as the radius of the medullary shell.

Dimensions.—Diameter of the disk 0.15 to 0.2, of the medullary shell 0.04 to 0.05; length of the radial spines 0.06 to 0.18, basal breadth 0.02 to 0.03.

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

9. Heliodiscus solaster, n. sp. (Pl. , fig. 4).

Disk with smooth surface, three times as broad as the medullary shell. Pores subregular, roundish; nine to ten on the radius. Marginal spines fifty to sixty, cylindro-conical, flexuose, very variable in size, the largest nearly as long as the diameter of the disk. The spines lie not only in the equatorial plane (as usual), but also in two to four crowded girdles on both sides of it.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the radial spines 0.05 to 0.15, basal breadth 0.008.

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

Subgenus 2. Heliodiscilla, Haeckel.

Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

10. Heliodiscus phacodiscus, Haeckel.

Heliodiscus phacodiscus, Haeckel, 1862, Monogr. d. Radiol., p. 437, Taf. xvii. figs. 5-7.

Haliomma phacodiscus, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 815.

Disk with spiny surface, three times as broad as the medullary shell. Pores regular, circular; six to eight on the radius. Marginal spines twelve to sixteen, conical, as long as the radius of the disk, and one-third as broad as the diameter of the medullary shell.

Dimensions.—Diameter of the disk 0.12 to 0.16, of the medullary shell 0.04 to 0.05; length of the marginal spines 0.06 to 0.08, basal breadth 0.01 to 0.02.

Habitat.—Mediterranean (Messina), Canary Islands (Lanzerote).

11. Heliodiscus amphidiscus, Haeckel.

Heliodiscus amphidiscus, Haeckel, 1862, Monogr. d. Radiol., p. 437.

Haliomma amphidiscus, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 154, Taf. ii. figs. 3-7.

Disk with spiny surface, three times as broad as the medullary shell. Pores regular, circular; eight to ten on the radius. Marginal spines twelve to fifteen, bristle-shaped, not larger than the surface spines, about as long as the radius of the medullary shell.

Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.05; length of the marginal spines 0.03, basal breadth 0.002.

Habitat.—Mediterranean (south shore of France), J. Müller.

12. Heliodiscus echiniscus, n. sp. (Pl. , fig. 5).

Disk with spiny surface, three times as broad as the medullary shell. Pores irregular, roundish or polygonal; eight to ten on the radius. Marginal spines thirty to fifty, pyramidal, angular, of very variable size, number, and disposition, gradually passing into the surface-spines; the largest nearly as long as the diameter of the medullary shell.

Dimensions.—Diameter of the disk 0.14, of the medullary shell 0.045; length of the radial spines 0.02 to 0.04, basal breadth 0.006.

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

13. Heliodiscus pertusus, n. sp. (Pl. , fig. 1).

Heliosestrum pertusum, Haeckel, 1881, Prodromus et Atlas (pl. xxxv. fig. 1).

Disk with spiny surface, three times as broad as the medullary shell. Pores irregular, circular, hexagonally framed; eight to ten on the radius. Marginal spines ten to thirty, very variable in size and disposition; commonly eight to twelve larger spines, which are pyramidal, about as long as the radius of the disk and perforated by two to four irregular, longish pores. Between these fenestrated large spines are commonly ten to twenty smaller conical spines, gradually passing into those of the surface.

Dimensions.—Diameter of the disk 0.13 to 0.16, of the medullary shell 0.04 to 0.05; length of the marginal spines 0.04 to 0.08, basal breadth 0.01 to 0.015.

Habitat.—North Pacific, Stations 241 to 244, depths 2300 to 2900 fathoms.

Subgenus 3. Heliodiscomma, Haeckel.

Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

14. Heliodiscus cingillum, n. sp. (Pl. , fig. 7).

Disk with smooth surface, five times as broad as the medullary shell. Pores regular, circular; twelve to fourteen on the radius. Equatorial girdle about as broad as the medullary shell, in the proximal half radially striped, on the margin with twenty to twenty-four short, flat, triangular spines, which are shorter than the breadth of the girdle.

Dimensions.—Diameter of the disk 0.25, of the medullary shell 0.05; length of the marginal spines 0.02, basal breadth 0.02.

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

15. Heliodiscus humboldti, Haeckel.

Heliodiscus humboldti, Haeckel, 1862, Monogr. d. Radiol., p. 438.

Haliomma humboldti, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 27; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxvii. fig. 3.

Haliomma humboldti, Bury, 1862, Polycystins of Barbados, pl. viii. fig. 3 (at left).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; eighteen to twenty on the radius. Equatorial girdle half as broad as the medullary shell, in the proximal half radially striped, on the margin with sixteen to twenty short, flat, triangular teeth, which are longer than the breadth of the girdle.

Dimensions.—Diameter of the disk 0.12 to 0.2, of the medullary shell 0.03 to 0.05; length of the marginal spines 0.02 to 0.04, basal breadth 0.02.

Habitat.—Fossil in Barbados (common and very variable).

16. Heliodiscus marginatus, n. sp. (Pl. , fig. 9).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; nine to ten on the radius. Equatorial girdle one-fourth to one-half as broad as the medullary shell, in the whole breadth radially striped, on the margin with twelve to eighteen very short and broad, triangular, marginal spines.

Dimensions.—Diameter of the disk 0.15 to 0.2, of the medullary shell 0.05 to 0.06; length of the marginal spines 0.01 to 0.02, basal breadth 0.02.

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

17. Heliodiscus sulcatus, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores subregular, circular; twelve to fifteen on the radius. Equatorial girdle as broad as the medullary shell, in the whole breadth radially striped on the margin with ten to fifteen triangular, deeply sulcated teeth, about as long and broad as the medullary shell. (Similar to Heliodiscus glyphodon, Pl. , fig. 2, but with broad sulcated girdle and shorter, more numerous spines.)

Dimensions.—Diameter of the disk 0.15 to 0.2, of the medullary shell 0.04 to 0.05; length of the radial spines 0.05 to 0.06, basal breadth 0.04 to 0.05.

Habitat.—Atlantic and Pacific, tropical part, many Stations, surface.

18. Heliodiscus umbonatus, Haeckel.

Haliomma umbonatum, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. fig. 4.

Disk with smooth surface, three times as broad as the medullary shell. Pores irregular, roundish; eight to ten on the radius. Equatorial girdle half as broad as the medullary shell, hyaline, not radially striped, on the margin with ten to twenty triangular, irregular, smooth teeth, very variable in size and disposition.

Dimensions.—Diameter of the disk 0.15 to 0.2, of the medullary shell 0.05 to 0.06; length of the marginal spines 0.02 to 0.08, basal breadth 0.01 to 0.03.

Habitat.—Cosmopolitan; Atlantic, Pacific, in various depths; also fossil in Barbados and Sicily.

Subgenus 4. Heliodiscura, Haeckel.

Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

19. Heliodiscus apollinis, n. sp.

Disk with spiny or bristly surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius. Equatorial girdle narrow, on the margin with sixteen to twenty broad, flat, triangular teeth, which are half as long and one-fourth as broad as the medullary shell. (Very similar to Astrophacus apollinis, Pl. , fig. 2, but with simple medullary shell.)

Dimensions.—Diameter of the disk 0.18, of the medullary shell 0.06; length of the marginal spines 0.03, basal breadth 0.015.

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

20. Heliodiscus zoroaster, n. sp.

Disk with spiny surface, four times as broad as the medullary shell. Pores subregular, circular; fourteen to sixteen on the radius. Equatorial girdle broad, radially striped, on the margin with ten to twelve pyramidal, deeply sulcated radial spines, which are nearly as long as the radius of the disk, and one-fourth as broad at the base.

Dimensions.—Diameter of the disk 0.24, of the medullary shell 0.06; length of the marginal spines 0.11, basal breadth 0.03.

Habitat.—Indian Ocean, between Aden and Ceylon, Haeckel, surface.

Genus 194. Heliodrymus, Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with simple medullary shell and with numerous (ten to twenty or more) branched radial spines on the margin of the disk (commonly with a variable number and an irregular disposition of the ramified spines).

The genus Heliodrymus differs from the nearly allied Heliodiscus by the ramification of the marginal spines, a character hitherto observed in no other genus of Phacodiscida. The branching is more or less irregular, either a simple bifurcation or a repeated fissure; the spines and their branches are commonly more or less flexuose. We can distinguish two subgenera: in Heliocladus the surface of the disk is smooth, in Heliodendrum covered with bristle-shaped radial spines, which are either simple or also branched, sometimes longer than the thick marginal spines.

Subgenus 1. Heliocladus, Haeckel, 1881, Prodromus, p. 457.

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

1. Heliodrymus dendrocyclus, n. sp. (Pl. , fig. 9).

Heliocladus dendrocyclus, Haeckel, 1881, Prodromus et Atlas (pl. xxxiii. fig. 9).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular, hexagonally framed; eight to nine on the radius. Marginal spines sixteen to twenty, cylindrical, very strong, flexuose, irregularly branched, nearly as long as the diameter of the disk. Between these main spines, each of which bears two to six irregular branches, are scattered on the margin numerous smaller simple spines.

Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.05; length of the main spines 0.1 to 0.14, breadth 0.01 to 0.02.

Habitat.—Central Pacific, Station 271, surface.

2. Heliodrymus furcatus, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius. Marginal spines twenty to twenty-five, cylindrical, flexuose, forked, about as long as the radius of the disk; fork-branches irregular, of unequal size. Some smaller simple spines are scattered between the forked ones.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.04; length of the radial spines 0.07 to 0.09, breadth 0.01.

Habitat.—Central Pacific, Station 265, surface.

3. Heliodrymus grottensis, Haeckel.

Heliodiscus grottensis, Stöhr, 1880, Palæontogr., vol. xxvi. p. 89, Taf. i. fig. 13.

Disk with smooth surface, two and a half times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Marginal spines twenty to thirty, conical, very irregular in form, size, and disposition; the smaller simple, the larger irregularly branched and half as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.17, of the medullary shell 0.07; length of the marginal spines 0.02 to 0.04, basal breadth 0.01 to 0.02.

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

Subgenus 2. Heliodendrum, Haeckel.

Definition.—Surface of the disk armed with simple or branched radial spines.

4. Heliodrymus setosus, n. sp.

Disk with spiny surface, four times as broad as the medullary shell. Pores regular, circular; twelve to thirteen on the radius. Marginal spines ten to twelve, cylindrical, irregularly branched, each with two to eight flexuose branches of different sizes; the largest as long as the diameter of the disk. Spines of the surface bristle-shaped, half as long, not branched.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the marginal spines 0.12 to 0.18, breadth 0.025.

Habitat.—North Pacific, Station 254, surface.

5. Heliodrymus ramosus, n. sp. (Pl. , figs. 3, 4).

Disk with spiny surface, three times as broad as the medullary shell. Pores regular, circular, hexagonally framed; eleven to twelve on the radius. Marginal spines sixteen to twenty, cylindrical, about as long as the radius, irregularly forked or branched, with unequal flexuose branches. Spines of the surface nearly as long, bristle-shaped, also irregularly branched.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the spines 0.06 to 0.08, basal breadth 0.01 to 0.015.

Habitat.—South Pacific, Station 288, surface.

6. Heliodrymus viminalis, n. sp. (Pl. , fig. 5).

Disk with spiny surface, two and a half times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius. Marginal spines fifteen to twenty, cylindro-conical, strong, partly simple, partly forked, about as long as the diameter of the disk. Spines of the surface very numerous, bristle-shaped, longer than the marginal spines, and more branched.

Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.06; length of the marginal spines 0.11 to 0.14, basal breadth 0.01 to 0.015; length of the surface spines 0.2 to 0.03.

Habitat.—Central Pacific, Station 271, surface.

Genus 195. Astrophacus, Haeckel, 1881, Prodromus, p. 457.

Definition.—Phacodiscida with double medullary shell and with numerous (ten to twenty or more) simple radial spines on the margin of the disk (commonly with a variable number and an irregular disposition of the undivided spines).

The genus Astrophacus differs from the similar Heliodiscus in the duplication of the medullary shell. The number and disposition of the radial spines of the margin (commonly between ten and twenty) is also here variable in one and the same species. The greater number of observed species of Astrophacus resemble in a very remarkable manner the corresponding species of Heliodiscus, and differ only in the double medullary shell.

Subgenus 1. Astrophacetta, Haeckel.

Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

1. Astrophacus asteriscus, n. sp.

Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; twelve to fourteen on the radius. Marginal spines fifteen to twenty, of variable size and disposition; the largest as long as the radius of the disk, as broad at the base as one pore. (Very similar to Heliodiscus asteriscus, Pl. , fig. 8, but differing in the double medullary shell.)

Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.025; length of the marginal spines 0.05 to 0.1, basal breadth 0.01.

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

2. Astrophacus trochiscus, n. sp. (Pl. , fig. 14).

Disk with smooth surface, three times as broad as the outer and seven times as broad as the inner medullary shell. Pores irregular, roundish; twelve to thirteen on the radius. Marginal spines sixteen to twenty, conical, of irregular variable size and disposition; the largest as long as the inner medullary shell. (Differs from Heliodiscus trochiscus in the double medullary shell.)

Dimensions.—Diameter of the disk 0.22, of the outer medullary shell 0.08, of the inner 0.03.

Habitat.—North Atlantic, Station 354, surface.

3. Astrophacus solaris, n. sp. (Pl. , fig. 1).

Disk with smooth surface, three times as broad as the outer and seven times as broad as the inner medullary shell. Pores subregular, roundish; twelve to fourteen on the radius. Marginal spines one hundred to one hundred and twenty, conical, flexuose, of irregular size and form; the largest one-third as long as the diameter of the disk. The spines lie not only in the equatorial plane (as is usual) but also in two to four crowded girdles on both sides of it. (Very similar to Heliodiscus solaster, Pl. , fig. 4, but of double the size, with double the number of spines and with a double medullary shell.)

Dimensions.—Diameter of the disk 0.3, of the outer medullary shell 0.11, of the inner 0.045; length of the spines 0.03 to 0.1, basal breadth 0.01 to 0.02.

Habitat.—Indian Ocean, Sunda Strait, Rabbe, surface.

Subgenus 2. Astrophacilla, Haeckel.

Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

4. Astrophacus phacodiscus, n. sp. (Pl. , fig. 3).

Disk with spiny surface, two and a half times as broad as the outer and seven times as broad as the inner medullary shell. Pores subregular, circular; ten to twelve on the radius. Marginal spines twelve to sixteen, conical, stout, nearly as long as the radius of the disk, and as broad at the base as the inner medullary shell. The numerous bristle-shaped spines of the surface are scarcely half as long. (Similar to Heliodiscus phacodiscus, Haeckel, Monogr. d. Radiol., Taf. xvii. figs. 5-7, but differing in the double medullary shell.)

Dimensions.—Diameter of the disk 0.18, of the outer medullary shell 0.07, of the inner 0.025; length of the marginal spines 0.08 to 0.09, basal breadth 0.03.

Habitat.—South Pacific, Station 300, surface.

Subgenus 3. Astrophacomma, Haeckel.

Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle. (Perhaps = Chilomma(?) Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.)

5. Astrophacus cingillum, n. sp.

Haliomma humboldti, var., Bury, 1862, Polycystins of Barbados, pl. viii. fig. 3 (at right).

Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; eleven to thirteen on the radius. Equatorial girdle about as broad as the inner medullary shell, in the proximal half radially striped, on the margin with eighteen to twenty-four short, flat, triangular spines, about as long as the breadth of the girdle. (Similar to Heliodiscus cingillum, but with double medullary shell.)

Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.025; length of the spines 0.02, basal breadth 0.02.

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

6. Astrophacus saturnus, Haeckel.

? Chilomma saturnus, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 297; 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 286, Taf. ii. fig. 5.

? Chilomma saturnus, Haeckel, 1862, Monogr. d. Radiol., p. 447.

Disk with smooth surface, two and a half times as broad as the outer, six times as broad as the inner medullary shell. Pores large, irregular, roundish; five to seven on the radius (?). Equatorial girdle very broad, radially striped, nearly as broad as the outer medullary shell, perforated by twenty to thirty (or more?) radial spines. (The position of this species, and the identity of Chilomma with Astrophacomma, remains doubtful, as the imperfect figure given by Ehrenberg of Chilomma saturnus, the only species of the genus, is in contradiction with his vague description, as is very often the case.)

Dimensions.—Diameter of the disk 0.12 (with girdle 0.22) of the outer medullary shell 0.05, of the inner 0.02.

Habitat.—Arctic Ocean (Greenland, depth 1000 fathoms), Ehrenberg.

Subgenus 4. Astrophacura, Haeckel.

Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

7. Astrophacus apollinis, n. sp. (Pl. , fig. 2).

Disk with spiny surface, three times as broad as the outer, eight times as broad as the inner medullary shell. Pores regular, circular; eleven to twelve on the radius of the disk. Equatorial girdle narrow, smooth, on the margin with twelve to sixteen broad, flat, triangular spines, of the same length as the numerous bristle-shaped spines of the surface, which reach half the radius of the disk. (Very similar to Heliodiscus apollinis, but differing in the double medullary shell.)

Dimensions.—Diameter of the disk 0.24, of the outer medullary shell 0.08, of the inner 0.03; length of the radial spines 0.06, basal breadth 0.03.

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