Thorax inflate, subspherical, truncate, with large, irregular, roundish pores, four to six times as large as those of the cephalis. Mouth constricted, flat, one-third as broad as the thorax.
Dimensions.—Cephalis 0.03 long, 0.04 broad; thorax 0.15 long, 0.18 broad.
Habitat.—Fossil in Barbados.
5. Sethocyrtis subacuta, Haeckel.
Shell smooth, pear-shaped, with sharp collar stricture. Length of the two joints = 1 : 4, breadth = 1 : 3. Cephalis subspherical, with small, irregular pores and a rudimentary horn of half the length. Thorax ovate, with large, subregular, hexagonal pores and thin bars between them. Mouth constricted, flat, half as broad as the thorax, without prominent peristome.
Dimensions.—Cephalis 0.02 long, 0.02 broad; thorax 0.08 long, 0.06 broad.
Habitat.—Philippine Sea, depth 3300 fathoms (Ehrenberg).
6. Sethocyrtis pleuracantha, Haeckel.
Shell smooth, bottle-shaped, with distinct collar stricture. Length of the two joints = 2 : 4, breadth = 1 : 3. Cephalis slenderly ovate, with an excentric pyramidal horn of the same length. Thorax inflate, ovate, with irregular, roundish pores and thin bars between them. Mouth constricted, flat, half as broad as the thorax, without prominent peristome.
Dimensions.—Cephalis 0.04 long, 0.02 broad; thorax 0.08 long, 0.06 broad.
Habitat.—Tropical Pacific, Stations 200, 225, 266, 274, &c., at various depths.
7. Sethocyrtis agamemnonis, n. sp. (Pl. 62, figs. 11, a, b).
Shell pear-shaped, rough, with sharp collar stricture. Length of the two joints = 2 : 10, breadth = 3 : 8. Cephalis subspherical, with very small pores and a small, pyramidal horn of half the length. Thorax inflate, ovate; in the uppermost part (beyond the collar stricture) with a ring of six to nine very large roundish pores, which are twice to four times as broad as the other irregular, roundish pores. (The shell is seen in fig. 11 from the apical pole, in fig. 11a with the cephalis, in fig. 11b without it, exhibiting the four central collar pores of the cortinar septum.) Mouth truncate, without prominent peristome.
Dimensions.—Cephalis 0.02 long, 0.03 broad; thorax 0.1 long, 0.08 broad.
Habitat.—North Pacific, Station 244, depth 2900 fathoms.
