Subfamily Cromyommida, Haeckel, 1881, Prodromus, pp. 449, 453

Definition.—Astrosphærida with four concentric spherical lattice-shells.

Genus 104. Cromyomma, Haeckel, 1881, Prodromus, p. 454.

Definition.—Astrosphærida with four concentric lattice-spheres and numerous simple radial spines of one kind.

The genus Cromyomma is the common ancestral form of the Cromyommida, or of those Astrosphærida in which the shell is composed of four concentric spheres, connected by radial beams. Usually two of these are intracapsular or medullary shells, two extracapsular or cortical shells; the distance between the former and the latter is greater than the distance between either the two inner or the two outer shells. In some cases, however (e.g., Cromyomma zonaster), the distance between all four shells is equal.

Subgenus 1. Cromyommetta, Haeckel.

Definition.—Pores of the outer cortical shell regular, of nearly equal size and similar form.

1. Cromyomma villosum, n. sp. (Pl. , fig. 2).

Radial proportion of the four spheres = 1 : 2 : 4 : 5. Outer cortical shell thick walled, densely covered with innumerable bristle-shaped radial spines, half as long as the radius. Pores regular, circular, double-edged, of the same breadth as the bars; ten to twelve on the radius. The thick outer shell is so dark, that the outlines only of the other three shells can be seen.

Dimensions.—Diameter of the four shells—(A) outer cortical shell 0.2, (B) inner cortical shell 0.16, (C) outer medullary shell 0.08, (D) inner medullary shell 0.04; pores and bars of the outer shell 0.008; length of the spines 0.04.

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

2. Cromyomma zonaster, Haeckel.

Acanthosphæra zonaster, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 285, Taf. ii. fig. 2.

Radial proportion of the four spheres = 2 : 3 : 4 : 5. Outer cortical shell thick walled, densely covered with numerous bristle-shaped radial spines, as long as the radius. Pores regular, circular, twice as broad as the bars; eight to ten on the radius. The thick outer shell is so dark, that the outlines only of the other three shells can be seen.

Dimensions.—Diameter of the four shells—(A) 0.15, (B) 0.12, (C) 0.09, (D) 0.06; pores of the outer shell 0.01, bars 0.005; length of the spines 0.08.

Habitat.—Arctic Ocean, Greenland (depth 1000 fathoms), "Alert" Expedition.

3. Cromyomma perplexum, Stöhr.

Cromyomma perplexum, Stöhr, 1880, Palæontogr., vol. xxvi. p. 95, Taf. iii. fig. 5.

Radial proportion of the four spheres = 1 : 2 : 3 : 4. Outer cortical shell thick walled, densely covered with short conical spines, as long as the diameter of the pores. These are regular, circular, three times as broad as the bars; six to eight on the radius. The thick outer shell is so dark, that the outlines only of the three other shells can be seen.

Dimensions.—Diameter of the four shells—(A) 0.17, (B) 0.13, (C) 0.087, (D) 0.043; pores of the outer shell 0.015, bars 0.005; length of the spines 0.02.

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

Subgenus 2. Cromyommura, Haeckel.

Definition.—Pores of the outer cortical shell irregular, of different size and form.

4. Cromyomma perspicuum, n. sp. (Pl. , fig. 8).

Cromyosphæra perspicua, Haeckel, 1879, Atlas (pl. xxx. fig. 8).

Radial proportion of the four shells = 1 : 2.5 : 6 : 9. Outer cortical shell very thin walled, with thread-like bars, and irregular, polygonal pores; inner cortical shell with similar pores, but with thicker bars. Both medullary shells with regular, circular pores (the outer three times as broad as the inner). Numerous thin radial beams connect the latter with the former; other very thin and numerous beams connect the two cortical shells, and are prolonged outside into short bristle-shaped spines (often longer than in the figure).

Dimensions.—Diameter of the four shells—(A) 0.18, (B) 0.12, (C) 0.05, (D) 0.02; pores of the outer shell 0.01 to 0.02; length of the spines 0.01 to 0.03.

Habitat.—Central Pacific, Station 274, surface.

5. Cromyomma quadruplex, Haeckel.

Cromyomma quadruplex, Haeckel, 1862, Monogr. d. Radiol., p. 446.

Haliomma quadruplex, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 243.

Radial proportion of the four spheres = 1 : 3 : 7 : 10. Outer cortical shell thin walled, irregularly covered with numerous angular spines, as long as the radius. Pores of all four shells irregular, roundish, increasing in size from the first to the fourth.

Dimensions.—Diameter of the four shells—(A) 0.15, (B) 0.1, (C) 0.045, (D) 0.015; pores of the outer shell 0.01 to 0.02; length of the spines 0.07.

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

6. Cromyomma macroporum, Stöhr.

Cromyomma macroporum, Stöhr, 1880, Palæontogr., vol. xxvi. p. 95, Taf. iii. fig. 4.

Radial proportion of the four spheres = 1 : 3 : 6 : 9. Outer cortical shell thick walled, densely covered with short conical spines, as long as the diameter of the pores; the latter are irregular, roundish, or polygonal, larger and smaller alternating.

Dimensions.—Diameter of the four shells—(A) 0.1, (B) 0.066, (C) 0.033, (D) 0.011; pores of the outer shell 0.033 to 0.016, bars 0.003; length of the spines 0.01.

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

7. Cromyomma circumtextum, n. sp. (Pl. , fig. 4).

Radial proportion of the four spheres = 1 : 2 : 5 : 7. Outer cortical shell very delicate and thin walled, with thread-like bars and large, irregular, polygonal meshes (larger than the innermost shell); inner cortical shell also with irregular, polygonal pores, three to nine times as broad as the thick bars. Both medullary shells with subregular, circular pores (the outer three times as broad as the inner). Radial spines twelve to twenty, three-sided prismatic, stout, piercing the three outer shells, inserted on the innermost; their outer part pyramidal, half as long as the radius.

Dimensions.—Diameter of the four shells—(A) 0.22, (B) 0.15, (C) 0.07, (D) 0.03; meshes of the outer shell 0.02 to 0.04; length of the outer spines 0.05.

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

8. Cromyomma mucronatum, n. sp. (Pl. , figs. 5, 5a).

Radial proportion of the three spheres = 1 : 2 : 3 : 6. Outer cortical shell thin walled, with large, irregular, roundish pores and crested three-sided bars; inner cortical shell with regular, circular, hexagonally formed pores (four times as broad as the bars). Both medullary shells with simple, small, regular, circular pores (fig. 5a). Twelve radial spines three-sided prismatic, dagger-shaped, with three teeth, as long as the diameter of the innermost shell.

Dimensions.—Diameter of the four shells—(A) 0.24, (B) 0.12, (C) 0.08, (D) 0.04; meshes of the outer shell 0.02 to 0.04; length of the spines 0.04.

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

Genus 105. Cromyechinus, Haeckel, 1881, Prodromus, p. 454.

Definition.—Astrosphærida with four concentric lattice-spheres and numerous simple spines of two different kinds; larger main spines and smaller by-spines.

The genus Cromyechinus differs from Cromyomma in the same way as Echinomma from Actinomma; the radial spines being differentiated into two different kinds; a larger number of small by-spines, and a smaller number of large main spines.

1. Cromyechinus icosacanthus, n. sp. (Pl. , fig. 1).

Radial proportion of the three spheres = 1 : 2 : 6 : 8. Outer cortical shell very delicate, with very small, regular, circular pores, covered with very numerous bristle-shaped by-spines, half as long as the radius; inner cortical shell with very large, irregular, polygonal pores, three to eight times as broad as the bars. Both medullary shells with regular, circular pores, connected with the former by twenty regularly disposed, very thin bars; these are prolonged outside into twenty very stout, three-sided prismatic main spines, as long as the radius, which arise from the inner cortical shell, and at the distal end are cuspidate.

Dimensions.—Diameter of the four shells—(A) 0.16, (B) 0.13, (C) 0.04, (D) 0.02; pores of the outer cortical shell 0.003, of the inner 0.03, bars 0.003; length of the spines 0.08.

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

2. Cromyechinus dodecacanthus, n. sp. (Pl. , figs. 3, 3a).

Radial proportion of the four spheres = 1 : 3 : 10 : 12. Outer cortical shell very delicate, with very small, regular, circular pores, covered with numerous short bristle-shaped by-spines, scarcely one-fourth as long as the radius; inner cortical shell with very large, irregular, polygonal pores, twice to six times as broad as the bars. Both medullary shells with very small, regular, circular pores, connected with the former by twelve regularly disposed, thin radial beams; these are prolonged outside into twelve strong, three-sided pyramidal main spines, one-third as long as the shell diameter. (Differs from the foregoing only in the number and form of the radial spines.)

Dimensions.—Diameter of the four shells—(A) 0.12, (B) 0.1, (C) 0.03, (D) 0.01; pores of the outer cortical shell 0.002, of the inner 0.02, bars 0.002; length of the spines 0.04, basal breadth 0.01.

Habitat.—South Atlantic, Station 325, surface.

3. Cromyechinus polyacanthus, n. sp.

Radial proportion of the four spheres = 1 : 2 : 8 : 10. Outer cortical shell of the same structure as the inner, with irregular, roundish pores, twice to six times as broad as the bars. Both medullary shells with small, regular, circular pores, twice as broad as the bars. Connecting radial beams forty to sixty, thin, cylindrical, prolonged outside into forty to sixty strong conical main spines, about as long as the radius. Between these, numerous thin bristle-shaped by-spines, nearly of the same length.

Dimensions.—Diameter of the four shells—(A) 0.25, (B) 0.2, (C) 0.05, (D) 0.025; pores of both cortical shells 0.01 to 0.03; length of the spines 0.12.

Habitat.—North Pacific, Station 237, surface.

Genus 106. Cromyodrymus, Haeckel, 1881, Prodromus, p. 454.

Definition.—Astrosphærida with four concentric lattice-spheres and numerous branched radial spines.

The genus Cromyodrymus differs from its ancestral form, Cromyomma, in the ramification of the radial spines, and exhibits therefore the same relation to it that Pityomma among the Actinommida bears to Actinomma.

1. Cromyodrymus quadricuspis, n. sp. (Pl. , figs. 7, 7a).

Radial proportion of the four shells = 1 : 3 : 6 : 12. All four shells with regular, circular pores, about twice as broad as the bars. Radial proportion of the pores in the four shells = 2 : 4 : 2 : 1. Radial spines fifty to sixty, three-sided prismatic, half as long as the radius, with three recurved teeth, each spine in this way bearing four points.

Dimensions.—Diameter of the four shells—(A) 0.16, (B) 0.08, (C) 0.04, (D) 0.013; length of the spines 0.03 to 0.04, breadth 0.007.

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

2. Cromyodrymus abietinus, n. sp. (Pl. , fig. 6).

Radial proportion of the four shells = 1 : 2 : 5 : 11. All four shells with irregular, roundish pores, twice to four times as broad as the bars. Radial proportion of the pores in the four shells = 9 : 3 : 2 : 1. Radial spines eighty to one hundred and twenty, about as long as the radius, branched like a pine tree, with six to twelve ramified branches.

Dimensions.—Diameter of the four shells—(A) 0.22, (B) 0.1, (C) 0.04, (D) 0.02; length of the spines 0.12, breadth 0.006.

Habitat.—South-east Pacific (Juan Fernandez), Station 299, surface.