The genus Tripterocalpis is distinguished from the other Archipilida by the remarkable combination of three lateral wings and of numerous (six to nine or more) terminal feet. It may be derived directly from the preceding Tripocalpis by multiplication of the terminal feet. These are sometimes obliquely directed. The central capsule is ellipsoidal or ovate, and fills up the greater part of the shell.
1. Tripterocalpis phylloptera, n. sp. (Pl. 51, fig. 1).
Shell slender, ovate, nearly twice as long as broad. Pores circular, of different sizes and at unequal distances. Along the lower half of the shell there arise three broad triangular lamellar wings. Peristome with twelve conical, nearly parallel and vertical feet, about one-sixth as long as the shell.
Dimensions.—Shell 0.2 long, 0.12 broad; wings 0.1 long, feet 0.03 long.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
2. Tripterocalpis conoptera, n. sp. (Pl. 51, fig. 2).
Shell ovate, nearly as broad as long. Pores regular, circular, quincuncial, twice as broad as the bars. In the middle of the shell there arise three conical, smooth, divergent wings, about half as long as the shell. Peristome with six short triangular, oblique, convergent feet.
Dimensions.—Shell 0.16 long, 0.14 broad; wings 0.09 long; feet 0.02 long.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
3. Tripterocalpis ogmoptera, n. sp. (Pl. 51, figs. 3-5).
Shell ovate, nearly as broad as long. Pores small and numerous, circular or roundish, partly confluent, double-contoured (fig. 4). In the middle of the shell there arise three very large conical divergent wings, which are longitudinally striped and longer than half the shell. Peristome with nine short triangular, oblique, convergent feet.
Dimensions.—Shell 0.18 long, 0.16 broad; wings 0.12 long, feet 0.02 long.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
Genus 499. Trissopilium,[1] Haeckel, 1881, Prodromus, p. 427.
Definition.—Archipilida (vel Monocyrtida triradiata aperta) with three lateral ribs or wings. Mouth smooth, without terminal feet. Apex with a horn.
The genus Trissopilium and the following nearly allied Archipilium differ from the other Archipilida in the absence of terminal feet, the peristome being quite simple, and truncate. But there are three lateral wings, arising either from the apex or from the lateral sides of the monothalamous shell. Trissopilium may perhaps be derived from Lithomelissa by reduction of the cephalis.
- ↑ Trissopilium = Small hat with three wings; τρίσσος, πίλιον.
