Page:Scientific results HMS Challenger vol 18 part 1.djvu/886

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Definition.—Surface of the shell with radial spines or thorns.

3. Tholocubus tesseralis, n. sp. (Pl. 10, fig. 16).

Surface of the shell with numerous (eight to sixteen) thin and long, bristle-shaped radial spines (the greater part broken off in the figured specimen); pores subregular, circular, three to four times as broad as the bars; ten to twelve in the semicircle of one cupola.

Dimensions.—Major axis of the shell 0.16, minor axis 0.14; pores 0.01, bars 0.0027.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Definition.— with double cortical shell (with external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the simple cuboidal central chamber (without medullary shell).

The genus Tholonium (Pl. 10, fig. 17) differs from the preceding Tholocubus only in the duplication of the cortical shell. The outer (secondary) shell forms either a simple (spheroidal or ellipsoidal) thin veil around the inner (primary) shell, or both shells are of the same form, with six corresponding cupolas. Possibly Tholonium is the offspring of Cubotholonium, having originated by loss of the medullary shell.

Definition.—Surface of the shell smooth or rough, without radial spines or thorns.

1. Tholonium bicubicum, n. sp.

Outer shell with six hemispherical dome-shaped protuberances, corresponding in those of the inner shell. Both shells connected by numerous radial beams. Surface of the outer shell smooth; its network nearly of the same shape as that of the inner, with subregular, circular pores, twice as broad as the bars; ten to fifteen pores on the semicircle of one cupola.

Dimensions.—Diameter of the outer shell 0.14, of the inner 0.12; pores of the latter 0.006, bars 0.003.

Habitat.—South Atlantic, Station 325, depth 2650 fathoms.