Shell with three } Columella simple, 506. _Archiscenium_. lateral lattice-wings, } connecting the three } Columella branched, 507. _Pteroscenium_. feet with the horn. } ------------------------------------------------------------------------- Shell with simple cavity, without free columella. Three free basal feet. ------------------------------------------------------------------------- One apical horn, 508. _Peridium_. Two or more horns, 509. _Archipera_. No apical horn, 510. _Archibursa_. Subfamily 1. ARCHIPILIDA, Haeckel, 1881, Prodromus, p. 427. _Definition._--#Tripocalpida# with the basal mouth of the shell open (vel Monocyrtida triradiata aperta). Genus 496. _Tripocalpis_,[113] Haeckel, 1881, Prodromus, p. 428. _Definition._--#Archipilida# (vel Monocyrtida triradiata aperta) with three lateral ribs prolonged into three terminal feet. Apex with a horn. The genus _Tripocalpis_ opens the series of Archipilida, or of those Monocyrtida in which the monothalamous shell exhibits a distinct triradial structure, and a simple open mouth, without cortinar lattice. _Tripocalpis_ is probably the most primordial of the Archipilida, and has three lateral ribs, which are prolonged into three free terminal {1136}feet, and connected in the apex of the pyramidal or campanulate shell with the apical horn. It may probably be derived from _Dictyophimus_ by loss of the cephalis. The central capsule is simple, spherical, or ellipsoidal. 1. _Tripocalpis plectaniscus_, n. sp. Shell three-sided pyramidal, smooth, about as long as broad, with irregular polygonal pores and thin bars. Apical horn stout, three-sided pyramidal, about as long as the shell. From the three edges of its base arise three prominent straight radial ribs, which are prolonged into three large divergent feet, of equal size and the same form as the horn. _Dimensions._--Shell 0.1 diameter, horn and feet 0.12. _Habitat._--Tropical Pacific (Philippine Sea), Station 206, depth 2100 fathoms. 2. _Tripocalpis galea_, Haeckel. _Halicalyptra galea_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. ii. fig. 10. Shell campanulate, rough, about as long as broad, with irregular roundish pores and thick bars. Apical horn stout, three-sided pyramidal, scarcely one-fourth as long as the shell. Beyond its base there arise three prominent, slightly curved lateral ribs, which are prolonged into three pyramidal, slightly divergent stout feet, somewhat shorter than the shell. _Dimensions._--Shell 0.08 to 0.09 diameter, horn 0.02, feet 0.07. _Habitat._--Fossil in Barbados. 3. _Tripocalpis tricostata_, n. sp.