campanulate with three slight swellings between the three knee-shaped ribs, and with regular, circular pores. Abdomen smaller, with three deep concave basal bays, and with irregular, roundish pores. Feet longer than the shell, slender, pyramidal, straight, parallel.
Dimensions.—Length of the three joints, a 0.02, b 0.04, c 0.02; breadth, a 0.02, b 0.07, c 0.07.
Habitat.—Indian Ocean, Ceylon (Haeckel); Zanzibar (Pullen).
8. Pterocanium depressum, Haeckel.
Shell (including the feet) nearly three-sided prismatic, rough. Length of the three joints = 1 : 2 : 1, breadth = 1 : 6 : 6. Cephalis subspherical, with a conical horn of the same length. Thorax a very flat and broad triangular pyramid, three times as broad as long. Abdomen smaller, with three deep, parabolic, concave bays. Pores irregular, roundish. Feet longer than the shell, slender, pyramidal, straight, parallel.
Dimensions.—Length of the three joints, a 0.02, b 0.04, c 0.02; breadth, a 0.025, b 0.12, c 0.12.
Habitat.—Indian Ocean, Zanzibar, depth 2200 fathoms (Pullen).
9. Pterocanium campanella, Haeckel.
Shell campanulate, smooth, with three high fenestrated crests and deep collar stricture. Length of the three joints = 1 : 3;1, breadth = 1 : 4 : 3. Cephalis subspherical, with a slender horn of the same length. Thorax inflated, campanulate, with three vaulted swellings between the three curved ribs. Abdomen short, with three semicircular bays between the three feet. Pores of the whole shell regular, circular, small, and numerous. Feet broad, triangular, shorter than the thorax, with convex back and convergent ends.
Dimensions.—Length of the three joints, a 0.015, b 0.06, c 0.2; breadth a 0.02, b 0.08, c 0.07.
Habitat.—Western Tropical Pacific, Philippine Sea, 3300 fathoms (Brooke).
10. Pterocanium tricolpum, n. sp. (Pl. 73, fig. 1).
Shell nearly three-sided prismatic, smooth, with three high fenestrated crests and two deep strictures. Length of the three joints = 1 : 3 : 2, breadth = 1 : 5 : 5. Cephalis subspherical, with an oblique, conical horn of the same length. Thorax inflated, with three highly vaulted bosoms between the three high crests, and with subregular, circular pores. Abdomen shorter, with three concave (or nearly rectangular, square) basal bays between the three feet, and with irregular, roundish pores, three to four pairs of larger pores occurring at the sides of the base of the feet. Feet nearly as long as the shell, with fenestrated bases, nearly straight and parallel; somewhat convergent, with convex back. (Often the concave bays between the three feet are not square, as in the specimen figured, but semi-
