Shell smooth, with slight collar stricture. Length of the two joints = 1 : 8, breadth = 1 : 5. Cephalis ovate, with a conical horn of half the length. Thorax pyramidal, with three sharp edges; its base prolonged into three pyramidal, divergent, hollow, fenestrated feet, nearly as long as the thorax. Pores regular, circular, double-contoured.
Dimensions.—Cephalis 0.04 diameter; thorax 0.2 diameter, length of the feet 0.15.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms; also fossil in Barbados.
4. Sethochytris triangula, Haeckel.
Lithochytris triangula, Bury, 1862, Polycystins of Barbados, pl. xix. fig. 7.
Shell rough, with obliterated collar stricture (but distinct internal collar septum). Length of the two joints = 1 : 6, breadth = 1 : 3. Cephalis subspherical, with a stout conical horn of the same length. Thorax pear-shaped, inflated; its base prolonged into three divergent, hollow, fenestrated cones, about as long as the thorax. Pores regular, circular.
Dimensions.—Cephalis 0.03 diameter; thorax 0.09 diameter, length of the feet 0.1.
Habitat.—Fossil in Barbados.
Genus 557. Clathrolychnus,[[174]] Haeckel, 1881, Prodromus, p. 431.
Definition.—Sethoperida (vel Dicyrtida triradiata clausa), with three vertical, lateral latticed wings stretched between the apical horn and the three terminal feet. The external lattice-work connecting the wings and closing the mouth forms an arachnoidal mantle around the shell.