Page:Scientific results HMS Challenger vol 18 part 2.djvu/286

1162 3. Cinclopyramis lithosestrum, n. sp.

Shell slender, pyramidal, with twelve strong radial ribs (six primary longer and six secondary shorter) connected by twelve to fifteen interrupted irregular rings. Meshes irregular square or trapezoidal, filled up by a delicate secondary network with irregular polygonal porules.

Dimensions.—Shell 0.4 to 0.5 long, 0.2 to 0.3 broad.

Habitat.—Fossil in Barbados.

Definition.— (vel Monocyrtida multiradiata aperta) with double, slenderly pyramidal shell, and numerous radial beams (six to nine or more). Network double, with an external arachnoidal or spongy envelope around the primary lattice-shell.

The genus Peripyramis differs from its probable ancestral form, Bathropyramis, by development of a delicate external envelope around the primary shell, and therefore bears to it the same relation that Spongopyramis among the Dicyrtida does to Sethopyramis. It may also be derived directly from the former by loss of the cephalis.

1. Peripyramis circumtexta, n. sp. (Pl. 54, fig. 5).

Shell slender, pyramidal, with nine strong radial beams, connected by fifteen to twenty transverse horizontal rings, which are partly complete, partly interrupted. Meshes subregular, square. From the nodal points of the surface there arise branched spines, which at equal distances from it are connected by thin threads, forming a delicate outer arachnoidal shell with large irregular polygonal meshes.

Dimensions.—Shell 0.32 long, 0.16 broad.

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

2. Peripyramis spongiosa, n. sp.

Shell slender, pyramidal, with nine strong radial beams, connected by twelve to eighteen irregular interrupted rings. Meshes irregular, square or polygonal. From the whole surface arise numerous branched spines, which by communication and dense ramification form an outer spongy envelope around the shell. (Similar to Spongopyramis spongiosa, Pl. 56, fig. 10.)

Dimensions.—Shell 0.45 long, 0.32 broad.

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