Page:Scientific results HMS Challenger vol 18 part 1.djvu/775

Rh delicate network (differs from Triopyle circulus by the production of the two convex latticed plates, which envelop the whole lens). Margin smooth.

Dimensions.—Diameter of the disk 0.045, of the gates 0.015.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

2. Triodiscus trigonus, n. sp.

Disk triangular, four times as broad as the central chamber. Three arm-chambers at the base half as broad, at the distal end twice as broad as the roundish gates. Surface smooth. On the three corners of the margin (in the arm-radius) three strong spines. (Differs from Triopyle trigona only in the loose framework closing the gates.)

Dimensions.—Diameter of the disk 0.04, of the gates 0.015.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

3. Triodiscus spinosus, n. sp. (Pl. 48, fig. 14).

Disk subcircular, four times as broad as the triangular central chamber. Three arm-chambers club-shaped, at the base one-third, at the distal end two-thirds as broad as the semicircular gates. Surface thorny. On the margin fifteen larger radial spines, three on the corners of the disk (in the radius of the gates), twelve on the two faces of the arms ends (two opposite on the edge of each end.) (Differs from Triopyle spinigera mainly by the delicate hexagonal network closing the gates.)

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

Habitat.—North Atlantic, Canary Islands (Lanzerote, Haeckel).

Definition.— with triopyle-shaped medullary shell, surrounded by three distal arm-chambers, which are separated by three open notches or gates.

Definition.— with triopyle-shaped medullary shell, surrounded by three distal arm-chambers. Notches between the three arms open.

The genus Pylolena opens the series of the Hexapylida, or of those Pylodiscida in which the centre of the shell is formed by a tri-radiated medullary shell like Triopyle. In the equatorial plane of this triopyle-shaped disk are developed on its margin three distal arm chambers, as prolongations of the three arms of Triopyle, but much larger. In Pylolene the three angles or notches between the distal arms remain open, repeating the form of Triolene.