Page:Scientific results HMS Challenger vol 18 part 2.djvu/833

Rh

Definition.— with four radial aboral feet and a variable number of circoral teeth.

The genus Tuscarusa differs from the preceding closely allied Tuscarora in the possession of four radial feet instead of three. The mouth of the single observed species is a narrow sagittal fissure, and armed with two opposite teeth (a dorsal and a ventral, as in the subgenus Tuscaretta). The four lateral feet form a cross, and lie opposite in pairs, in two diagonals of the square, which is bisected by the sagittal mouth.

1. Tuscarusa medusa, n. sp. (Pl. 100, figs. 7, 7a).

Shell ovate, with four crossed lateral feet in the upper third, and with two opposite teeth around the mouth. The four feet are opposite in pairs in two diameters of the shell, perpendicular one to another, and arise between the upper and middle third of the shell; they are thin, cylindrical, spinulate, arcuate, and ascend to the height of the mouth diverging upwards; then they are curved downwards in a large arc. They lie in the diagonals of the square, which is halved by the narrow and long fissure of the mouth. This lies in the original sagittal plane, and from its two corners arise the two opposite teeth (a dorsal and a ventral), diverging upwards, cylindrical and slightly curved. The base of each foot is pierced by four pedal pores, of each tooth by two dental pores.

Dimensions.—Length of the shell 1.2, breadth 1.0.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

Definition.— without radial aboral feet, but with a terminal axial caudal foot, and a variable number of circoral teeth.

The genus Tuscaridium, comprising two closely allied species, differs from the two preceding genera of Tuscarorida in the absence of lateral radial feet, which are represented by a single large caudal spine placed in the main axis of the shell, at its aboral pole. The shell is therefore spindle-shaped, and not ovate or subspherical, as in the two other genera. It reaches in the two observed species a length of more than 3 mm.

1. Tuscaridium cygneum, Haeckel.

Tuscarora cygnea, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 20.

Shell spindle-shaped, twice as long as broad (in the transverse section circular), equally tapering towards both poles of the main axis. The aboral pole bears a thin, cylindrical, straight, caudal