Definition.—Archipilida (vel Monocyrtida triradiata aperta) with three lateral ribs or wings. Mouth truncate, without terminal feet. Apex without horn.
The genus Archipilium differs from the nearly allied Trissopilium, its probable ancestral form, in the absence of the apical horn. The three lateral wings of the ovate shell are stout spines. It may also be derived from the similar Sethopilium by reduction and loss of the cephalis.
1. Archipilium orthopterum, n. sp. (Pl. [98], fig. 7).
Shell ovate, smooth, nearly cylindrical, scarcely broader than the truncate, widely open mouth. Pores numerous, irregular, roundish, of very different sizes. Three lateral wings arising from the middle zone, twice as long as the shell, straight, divergent, stout, cylindrical, longitudinally striped.
Dimensions.—Shell 0.08 long, 0.06 broad; wings 0.15 long.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
2. Archipilium sigmopterum, n. sp.
Shell ovate, smooth, nearly campanulate, of equal length and breadth, one and one-third times as broad as the truncate, slightly constricted mouth. Pores scarce, irregularly formed and 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.