Page:Scientific results HMS Challenger vol 18 part 2.djvu/326

1202 2. Tripocyrtis tripodiscus, n. sp.

Cephalis subspherical, with small, polygonal pores and a large, arborescent, vertical horn of thrice the length, bearing numerous ramified branches. Thorax with three straight, widely divergent ribs, of the same length as the horn, connected by a delicate, arachnoidal framework with irregular, polygonal meshes.

Dimensions.—Cephalis 0.04 long, 05 broad; thorax 0.12 long, 0.18 broad.

Habitat.—Central Pacific, Station 269, surface.

3. Tripocyrtis plectaniscus, n. sp. (Pl. 60, fig. 9).

Cephalis subspherical, with small roundish pores, and a stout, three-sided pyramidal, denticulate horn of the same length. Thorax with three little divergent and curved ribs, twice as long as the horn, in the upper half with smaller, in the lower half with larger, polygonal, irregular meshes.

Dimensions.—Cephalis 0.05 long, 0.06 broad; thorax 0.1 long, 0.12 broad.

Habitat.—Central Pacific, Station 264, surface.

Definition.— (vel Dicyrtida triradiata aperta) with three complete thoracic ribs, which are prolonged into three solid divergent feet on the peristome. Cephalis smooth, without a horn.

The genus Sethopilium differs from its probable ancestral form Dictyophimus by the complete loss of the cephalic horn, and of the collar septum between both joints, which are only separated by the slight external collar stricture.

1. Sethopilium orthopus, n. sp. (Pl. 97, fig. 8).

Shell smooth, with sharp collar stricture, Relative length of the two joints = 5 : 4, breadth = 7 : 6. Cephalis large, subspherical, with numerous regular circular pores, twice as broad as the bars. Thorax with three stout, straight, widely divergent ribs, prolonged into three straight pointed feet of the same length. Between every two ribs, in the centre of the collar stricture, a single large triangular mesh, and beyond this three to six rows of smaller irregular meshes.

Dimensions.—Cephalis 0.05 long, 0.07 broad; thorax 0.04 long, 0.06 broad.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Sethopilium cyrtopus, n. sp.

Shell smooth, with sharp collar stricture. Relative length of the two joints = 4 : 6, breadth = 7 : 11. Cephalis hemispherical, with large irregular roundish pores, four times as broad as the bars.