Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
Genus 615. Theocyrtis,[[232]] n. gen.
Definition.—Theocorida (vel Tricyrtida eradiata aperta) with cylindrical abdomen, and wide open truncate mouth. Cephalis with a single horn.
The genus Theocyrtis and the three following closely allied genera differ from the other Theocorida in the cylindrical form of the slender abdomen, which is of equal breadth nearly throughout its whole length. The terminal mouth is wide open, usually truncate, and of the same breadth; sometimes slightly constricted. The cephalis of Theocyrtis bears a single horn.
Subgenus 1. Theocorypha, Haeckel.
Definition.—Pores of the thorax and abdomen of nearly equal size and similar form.
1. Theocyrtis trachelius, Haeckel.
Eucyrtidium trachelius, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 293, Taf. vii. fig. 8.
Shell thin-walled and very fragile, smooth. Length of the three joints = 2 : 8 : 7, breadth = 2 : 9 : 8. Cephalis subspherical, with a straight, conical horn of the same length, separated by a slender neck from the inflated, subspherical thorax. Abdomen cylindrical, with a wide open, truncate mouth. Pores subregular, hexagonal, of equal size, four to six times as broad as the thin, thread-like bars.
Dimensions.—Length of the three joints, a 0.02, b 0.08, c 0.07; breadth, a 0.02, b 0.09, c 0.08.