Spongy framework denser and darker in the central part of the sphere than in the peripheral part, with rather coarse meshes and thick bars. From the surface arise very numerous (sixty to eighty) stout, radial branches, as long as the shell radius, branched like a pine tree (with six to twelve ramified branches). Similar in structure to Cromyodrymus abietinus (Pl. [30], fig. 6), but with a quite irregular spongy texture in the central sphere.
Dimensions.—Diameter of the sphere 0.3; length of the spines 0.015.
Habitat.—Central Pacific, Station 272, surface.
Genus 113. Spongechinus,[[152]] Haeckel, 1881, Prodromus, p. 456.
Definition.—Astrosphærida with hollow, spongy sphere, without latticed medullary shell in the central cavity, and with numerous simple radial spines.
The genus Spongechinus differs from its ancestral form, Plegmosphæra, in the development of numerous radial spines on the surface of the spongy sphere, within which is enclosed a large spherical central cavity.
1. Spongechinus setosus, n. sp.
Spongy sphere three times as broad as its inner cavity, with a very delicate, equal framework. Entire surface covered with short, straight, bristle-shaped radial spines, about half as long as the radius.
Dimensions.—Diameter of the sphere 0.2, of its inner cavity 0.07; length of the spines 0.05.
Habitat.—North Atlantic, Azores, surface.