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.
Genus 501. Tripilidium,[[118]] Haeckel, 1881, Prodromus, p. 428.
Definition.—Archipilida (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).
Subgenus 1. Tristylocorys, Haeckel.
Definition.—Feet simple, not branched.
1. Tripilidium cortina, n. sp.