Genus 104. Cromyomma,[[141]] 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. [30], 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.