Definition.—All three rings equal, circular.
4. Trissocircus octahedrus, n. sp.
All three rings equal, circular, smooth, their rods cylindrical (in the transverse section circular). From each pole of the three equal axes arises a short conical spine; these six spines correspond to the six corners of a regular octahedron.
Dimensions.—Diameter of all three rings 0.08, thickness 0.006.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
5. Trissocircus globus, n. sp. (Pl. [82], fig. 13).
All three rings equal, circular, thorny; their rods prismatic (in the transverse section triangular), with three sharp dentated edges and scattered branched thorns. From each pole of the three equal axes (which correspond to the three axes of a regular octahedron) arises a bunch of larger spines.
Dimensions.—Diameter of all three rings 0.12, thickness 0.01.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.