Page:Scientific results HMS Challenger vol 18 part 2.djvu/134

1010 2. Prismatium tripleurum, Haeckel.

Prismatium tripleurum, Haeckel, 1862, Monogr. d. Radiol., p. 270, Taf. iv. fig. 6.

Acanthodesmia prismatium, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 799.

Mitral and basal rings of equal size, equilateral triangular, both connected at the corners by three vertical equal columellæ. From the six corners arise six short, equal, conical radial spines. The nine rods of the shell correspond to the nine edges of a triangular equilateral prism.

Dimensions.—Length of the shell 0.044, breadth 0.032.

Habitat.—Mediterranean (Messina), surface.

Definition.— with two simple horizontal rings of different sizes, connected by four divergent columellæ.

The genus Pseudocubus exhibits the characteristic form of an obelisk, or a truncated four-sided pyramid. The four edges of this obelisk, or the four "columellæ," are the remaining parts of the two incomplete vertical rings; two opposite edges are the dorsal and ventral rod of the sagittal ring; the two alternate edges between these are the lateral rods of the frontal ring. The two horizontal rings, which become connected by the four divergent columellæ, are the smaller mitral ring and the larger basal ring; both are either square or nearly circular.

1. Pseudocubus obeliscus, n. sp. (Pl. 94, fig. 11).

Mitral ring square, with circular gate and two divergent simple spines on each corner. Basal ring twice as broad, square, with four convex sides and one simple spine on each corner. Four columellæ straight. All twelve rods with three smooth edges.

Dimensions.—Breadth of the mitral ring 0.02, of the basal ring 0.05.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Pseudocubus octostylus, n. sp.

Mitral ring square, with one stout pyramidal spine on each corner. Basal ring twice as broad, square, also with a single strong spine on each corner. Four columellæ straight. All twelve rods with three smooth edges.

Dimensions.—Breadth of the mitral ring 0.04, of the basal ring 0.08.

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