Page:Scientific results HMS Challenger vol 18 part 1.djvu/821

Rh

Definition.— with spongy lentelliptical shell (with or without enclosed medullary shell).

Definition.— with lentelliptical spongy shell, containing a central cavity of the same form, without medullary shell (without radial spines).

The genus Spongolarcus differs from Cenolarcus (its probable ancestral form) only in the development of spongy framework forming the wall of the hollow lentelliptical shell. It corresponds, therefore, to Plegmosphæra among the, and to Spongellipsis among the. From these two similar spongy it differs in its characteristic lentelliptical form, with three dimensive axes of unequal length.

1. Spongolarcus lentellipsis, n. sp.

Spongy network of the shell very loose, its meshes fifteen to twenty times as broad as the bars. Surface of the shell nearly smooth; diameter of its internal cavity twice as large as the thickness of its wall. Proportion of the three dimensive axes = 2 : 3 : 4.

Dimensions.—Length 0.16, breadth 0.12, height 0.08; thickness of the spongy wall 0.05.

Habitat.—Pacific, central area, Station 274, surface.

2. Spongolarcus triaxonius, n. sp.

Spongy network of the shell rather loose, its meshes twelve to sixteen times as broad as the bars. Surface of the shell rough; diameter of its internal cavity about eight times as large as the thickness of its wall. Proportion of the three dimensive axes = 2 : 2.5 : 3.

Dimensions.—Length 0.25, breadth 0.2, height 0.16; thickness of the spongy wall 0.025.

Habitat.—North Pacific, Station 253, surface.

3. Spongolarcus dimensivus, n. sp.

Spongy network of the shell dense, its meshes four to eight times as broad as the bars. Surface of the shell thorny; diameter of its internal cavity about fifteen times as large as the thickness of its wall. Proportion of the three dimensive axes = 3 : 4 : 5.

Dimensions.—Length 0.2, breadth 0.16, height 0.12; thickness of the spongy wall 0.01.

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