Page:Scientific results HMS Challenger vol 18 part 2.djvu/363

Rh 3. Tetrahedrina quadricornis, Haeckel.

Lithochytris triangula, Bury, 1862, Polycystins of Barbados, pl. xix. figs. 4, 5, 6.

Shell pear-shaped, papillate, with slight collar stricture. Length of the two joints = 1 : 5, breadth = 1 : 5. Cephalis subspherical, with a stout conical horn twice the length. Thorax with irregular, roundish, lobulated pores, with three conical, stout, divergent feet at the base, of the same size and form as the cephalic horn.

Dimensions.—Cephalis 0.02 diameter; thorax 0.1 long, 0.1 broad.

Habitat.—Fossil in Barbados.

Definition.— (vel Dicyrtida triradiata clausa) with three terminal latticed feet or hollow, fenestrated, divergent, basal apophyses of the thorax. Cephalis with a horn.

The genus Sethochytris differs from the preceding Tetrahedrina in the fenestration of the three basal feet, which form direct protrusions or evaginations of the three basal corners of the pyramidal shell. It may be derived from Sethopera by centrifugal growth of the basal corners.

1. Sethochytris triconiscus, n. sp. (Pl. 57, fig. 13).

Shell rough, with deep collar stricture. Length of the two joints = 1 : 8, breadth = 1 : 3. Cephalis spherical, with an oblique pyramidal horn of the same length. Thorax campanulate, conical; its three basal corners prolonged into three divergent, slender, hollow, fenestrated cones, twice as long as the thorax, and ending in a stout pyramidal spine.

Dimensions.—Cephalis 0.04 diameter, thorax 0.12 diameter, length of the feet 0.2.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

2. Sethochytris barbadensis, Haeckel.

Lithochytris barbadensis, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 160, Taf. v. fig. 2.

Shell smooth, with slight collar stricture. Length of the two joints = 1 : 6, breadth = 1 : 4. Cephalis ovate, with a conical horn of half the length. Thorax conical; its base prolonged into three divergent, hollow, fenestrated cones, half as long as the thorax. Pores small, subregular, circular.

Dimensions.—Cephalis 0.025 diameter, thorax 0.1 diameter, length of the feet 0.05.

Habitat.—Fossil in Barbados.