The genus Tricolocapsa differs from the preceding Theocapsa in the loss of the apical horn, and exhibits therefore to it the same relation that Theocampe bears to Theocorys. In some species (Pl. 66, figs. 1, 3) a small tube begins to be developed on the cephalis, and these may perhaps be separated as a peculiar genus, Tricolopera.
Subgenus 1. Tricolocapsula, Haeckel.
Definition.—Thorax of about the same size as the abdomen, or larger.
1. Tricolocapsa theophrasti, n. sp. (Pl. 66, fig. 1).
Shell slenderly ovate, with two slight strictures. Length of the three joints = 2 : 8 : 5, breadth = 3 : 7 : 5. Cephalis hemispherical, with a larger, tube-like, cervical pore at the collar stricture. Thorax very thick-walled, with irregular, roundish, double edged pores, smaller than the bars between them. Abdomen smaller, inversely campanulate-conical, with very irregular pores. Basal pole acute.
Dimensions.—Length of the three joints, a 0.02, b 0.08, c 0.05; breadth, a 0.03, b 0.07, c 0.05.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
2. Tricolocapsa dioscoridis, n. sp. (Pl. 66, fig. 3).
Shell short and broad, with two deep strictures. Length of the three joints = 3 : 5 : 4, breadth = 4 : 7 : 5. Cephalis hemispherical, with a larger, tube-like, cervical pore above the collar stricture. Thorax very broad, with irregular, large and spare, roundish pores. Abdomen much smaller, inversely conical, with smaller pores. Basal pole obtuse.
Dimensions.—Length of the three joints, a 0.03, b 0.05, c 0.04; breadth, a 0.04, b 0.07, c 0.05.
Habitat.—Central Pacific, Station 274, depth 2750 fathoms.
3. Tricolocapsa linnæi, n. sp. (Pl. 66, fig. 5).
Shell short and broad, with two deep strictures. Length of the three joints = 1 : 4 : 2, breadth = 1 : 4 : 2. Cephalis hemispherical. Thorax thick-walled, inflated, with subregular, circular, double-edged pores. Abdomen much smaller, thin-walled, with irregular, polygonal pores. Basal pole hemispherical, rounded.
Dimensions.—Length of the three joints, a 0.02, b 0.08, c 0.05; breadth, a 0.03, b 0.08, c 0.05.
Habitat.—South Pacific, Station 295, depth 1500 fathoms.
