The genus Sethocyrtis and the three following nearly allied genera differ from the three preceding genera of Sethocorida in the form of the thorax, which is not gradually dilated, conical, but cylindrical or ovate, with more or less constricted mouth. Sethocyrtis may be derived from Anthocyrtis by loss of the terminal feet. Its mouth is quite simple, without tubular or annular peristome.
1. Sethocyrtis oxycephalis, n. sp. (Pl. 62, fig. 9).
Shell rough, subconical, with slight collar stricture. Length of the two joints = 4 : 9, breadth = 3 : 8. Cephalis ovate, with a pyramidal horn of half the length. Thorax campanulate, with regular, circular pores, twice as broad as those of the cephalis. Mouth constricted, scarcely half as broad as the thorax.
Dimensions.—Cephalis 0.04 long, 0.03 broad; thorax 0.09 long, 0.08 broad.
Habitat.—Central Pacific, Stations 263 to 274, depth 2350 to 3000 fathoms.
2. Sethocyrtis cancrina, Haeckel.
Shell smooth, bottle-shaped, with obliterated collar stricture. Length of the two joints = 4 : 9, breadth = 2 : 7. Cephalis subcylindrical, with a stout conical horn of the same length, and sometimes a smaller accessory horn at its base. Thorax ovate, truncate, with regular, circular, quincuncial pores, twice as broad as those of the cephalis. Mouth little constricted, flat, nearly as broad as the thorax.
Dimensions.—Cephalis 0.04 long, 0.02 broad; thorax 0.09 long, 0.07 broad.
Habitat.—Fossil in Barbados.
3. Sethocyrtis diomedis, n. sp.
Shell thorny, pear-shaped, with slight collar stricture. Length of the two joints = 3 : 16, breadth = 4 : 20. Cephalis hemispherical, with a conical horn of twice the length. Thorax inflate, ovate, truncate at both poles, with regular, circular pores, twice as broad as those of the thorax. Mouth constricted, flat, half as broad as the thorax.
Dimensions.—Cephalis 0.03 long, 0.04 broad; thorax 0.12 to 0.16 long, 0.16 to 0.2 broad.
Habitat.—Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms; also fossil in Barbados.
4. Sethocyrtis menelai, n. sp.
Shell spiny, pear-shaped, with sharp collar stricture. Length of the two joints = 3 : 15, breadth = 4 : 18. Cephalis subspherical, with a large, cylindro-conical horn, about as long as the whole shell.
