Page:Scientific results HMS Challenger vol 18 part 2.djvu/267

Rh

Definition.— (vel Monocyrtida triradiata aperta) without lateral ribs and apical horn, with three simple or branched terminal feet.

The genus Tripodiscium may be derived either from the preceding Tripilidium by loss of the apical horn, or from the nearly related Tristylospyris by loss of the sagittal ring and constriction. Some forms of the latter genus can scarcely be distinguished from similar species of the former.

Definition.—Feet simple, not branched nor forked.

1. Tripodiscium tristylospyris, n. sp.

Shell subspherical, with regular, circular pores, twice as broad as the bars. Mouth constricted, half as broad as the shell, with three short spindle-shaped feet, which are nearly parallel and vertical, half as long as the shell. (Similar to Tristylospyris scaphipes, Pl. 84, fig. 13, but without sagittal ring and constriction.)

Dimensions.—Shell 0.08 long, 0.07 broad; feet 0.04 long.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

2. Tripodiscium ovatum, n. sp.

Shell ovate, rough, nearly as broad as long. Pores regular circular, double-contoured, twice as broad as the bars. Mouth constricted, one-third as broad as the shell, with three convergent short triangular feet.

Dimensions.—Shell 0.1 long, 0.09 broad; feet 0.02 long.

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

3. Tripodiscium clavatum, n. sp.

Shell ovate, smooth, one and a half times as long as broad. Pores irregular roundish, of different sizes. Mouth constricted, two-thirds as broad as the shell, with three divergent, straight club-shaped feet, nearly as long as the shell.

Dimensions.—Shell 0.12 long, 0.08 broad; feet 0.1 long.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.