Page:Scientific results HMS Challenger vol 18 part 1.djvu/481

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Definition.— 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.

2. Spongechinus serrulatus, n. sp.

Spongy sphere twice as broad as its inner cavity, with a delicate, equal framework. Entire surface covered with short, curved, radial spines, which are elegantly denticulated, and as long as the shell radius.

Dimensions.—Diameter of the sphere 0.3, of its cavity 0.15; length of the spines 0.15.

Habitat.—Central Pacific, Station 274, surface.

3. Spongechinus cavus, n. sp.

Spongy sphere only one-fourth broader than the large inner cavity, its spongy wall being only one-fourth as thick as the radius, composed of three to four strata of irregular, small meshes. Surface covered with short, bristle-shaped, curved spines, one-third as long as the radius.

Dimensions.—Diameter of the sphere 0.5, of its inner cavity 0.4; length of the spines 0.08.

Habitat.—North Atlantic, Station 354, surface.

Definition.— with hollow, spongy sphere, without latticed medullary shell in the central cavity, and with numerous branched radial spines.

The genus Spongothamnus differs from the preceding Spongechinus in the ramification of the numerous radial spines, covering the surface of the hollow spongy sphere;