1138 THE VOYAGE OF H.M.S. CHALLENGER. 



The genus Tripterocalpis is distinguished from the other Archipilida by the remark- 

 able combination of three lateral \\4ngs and of numerous (six to nine or more) terminal 

 feet. It may be derived directly from the preceding Tripodocalpis 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 sleuder, ovate, nearly twice as long as broad. Pores circular, of difterent sizes and at 

 unequal distances. Along the lower half of the shell there arise three broad triangular lamellar wings. 

 Peristome with twelve conical, nearly jjarallel and vertical feet, about one-sixth as long as the shell. 



Dimeimans. — Shell 0'2 long. 012 broad; wings O'l long, feet 0'03 long. 



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



2. Tripterocalpis conoptera, n. sp. (PI. 51, fig. 2). 



Shell ovate, nearly as broad as long. Pores regular, circular, quincimcial, 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, obUque, convergent feet. 



Dimensions. — Shell 016 long, 014 broad ; wings 0'09 long ; feet 002 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 lune short triangular, oblique, convergent feet. 



Divunsions. — Shell 018 long, 016 broad ; wings 012 long, feet 0"02 long. 



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



Genus 499. Trissopilium,^ Haeckel, 1881, Prodromus, p. 427. 



Definition. — A r c h i p i 1 i d a (vel Monocyrtida triradiata aperta) with three lateral 

 ribs or wings. Mouth smooth, without terminal feet. Apex with a horn. 



The genus Trissojnlium and the following nearly allied Archipilium differ from the 

 i)ther Ai'chipilida 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 = SmuW hat witli three winga ; Tf/ujof, r^i'htov. 



