Page:Scientific results HMS Challenger vol 18 part 1.djvu/1089

Rh 3. Hexacolpus trypanon, n. sp. (Pl. 140, fig. 11).

Six hydrotomical spines of unequal size, two equatorial about as long as the diameter of the shell and nearly twice as large as the four polar; all of the same form, quadrangular prismatic, with prominent edges and pointed distal ends. Sheaths six-sided prismatic, with strong prominent edges and thinner parallel ribs between them; their distal mouth with six strong denticulated teeth. The sheaths envelop two-thirds of the spines, and are as broad as the radius of the shell.

Dimensions.—Diameter of the shell 0.13; length of the equatorial spines 0.12, of their sheaths 0.08; breadth of the latter 0.06.

Habitat.—South Pacific, Station 288, surface.

4. Hexacolpus dodecodus, n. sp.

Six hydrotomical spines of unequal size, two equatorial about as long as the radius of the shell and twice as large as the four polar; all of the same form, triangular, compressed, sulcated. Sheaths prismatic, with twelve prominent, parallel edges, and twelve strong serrated triangular teeth on the mouth. The sheaths envelop the basal half of the spines. This species greatly resembles Hexaconus serratus (Pl. 139, fig. 4), but differs in the larger size of the equatorial spines and the complete reduction of the fourteen smaller spines.

Dimensions.—Diameter of the shell 0.2; length of the equatorial spines 0.1, of their sheaths 0.06; breadth of the latter 0.08.

Habitat.—North Pacific, Station 248, surface.

5. Hexacolpus infundibulum, n. sp. (Pl. 140, fig. 10).

Six hydrotomical spines of unequal size, two equatorial about twice as long as the diameter of the shell and as the four polar spines; all six spines of the same form, quadrangular prismatic, pointed at the distal pyramidal end. Sheaths conical, two to three times as broad at the denticulate distal mouth as at the narrow base, sulcate; the mantle of the cone concavely vaulted. The large sheaths envelop two-thirds or three-fourths of the spines.

Dimensions.—Diameter of the shell 0.1 to 0.13; length of the equatorial spines 0.15 to 0.2, of their sheaths 0.1 to 0.15; basal breadth of the latter 0.04, distal breadth 0.12.

Habitat.—Central Pacific, Station 272, surface.

Definition.— with simple diploconical shell, composed of two very large equatorial spines which are opposite in the hydrotomical axis, are surrounded by conical or cylindrical, often compressed sheaths, and arise from a small central