_Dimensions._--Shell 0.12 long, 0.09 broad; feet 0.06 long. _Habitat._--Central Pacific, Station 266, depth 2750 fathoms. Genus 498. _Tripterocalpis_,[115] Haeckel, 1881, Prodromus, p. 428. _Definition._--#Archipilida# (vel Monocyrtida triradiata aperta) with three lateral wings and a peristomial corona of numerous terminal feet. Shell ovate, with constricted mouth, without apical horn. {1138}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_,[116] 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. {1139}1. _Trissopilium tetraplecta_, n. sp.