Page:Scientific results HMS Challenger vol 18 part 2.djvu/264

1140 scattered, of very different sizes. Three lateral wings, stout, prismatic, about as long as the shell widely divergent and S-shaped, curved.

Dimensions.—Shell 0.08 diameter, wings 0.08 long.

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

3. Archipilium cyrtopterum, n. sp.

Shell ovate, rough, twice as broad as the constricted mouth. Pores small and numerous, subregular, circular, smaller than the bars. Three lateral wings cylindrical, crescentic, in the upper half divergent, in the lower convergent, one and one-half times as long as the shell.

Dimensions.—Shell 0.09 long, 0.07 broad; wings 0.14 long.

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

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

The genus Tripilidium differs from Tripodonium in the absence of the three lateral ribs, and may be derived either from this ancestral form, or directly from Tripospyris (by loss of the sagittal ring and constriction); perhaps also from Lychnocanium (by reduction of the cephalis). We distinguish as two subgenera, Tristylocorys (with simple feet) and Tripodocorys (with branched feet).

Definition.—Feet simple, not branched.

1. Tripilidium cortina, n. sp.

Shell campanulate, rough, about as long as broad. Pores subregular, circular, larger in the middle zone, twice to three times as broad as the bars. Mouth constricted, half as broad as the shell. Apical horn straight and stout, three-sided pyramidal, about as long as the shell. Three feet divergent, slightly S-shaped, curved, somewhat longer the the shell.

Dimensions.—Shell 0.1 diameter, horn 0.09 long, feet 0.13 long.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

2. Tripilidium hemisphæricum, n. sp.

Shell hemispherical, smooth, nearly twice as broad as long. Pores large, with thin bars, irregular, roundish, of very different sizes. Mouth wide open. Apical horn conical, half as long as