Page:Scientific results HMS Challenger vol 18 part 2.djvu/373

Rh arise, alternating with the former, directly from the horizontal collar ring; eight ribs are adradial or tertiary, and arise in pairs from the four large perradial basal arches of the thorax, which become bisected by the four primary ribs. Peristome irregularly denticulate.

Dimensions.—Cephalis 0.02 long, 0.06 broad; thorax 0.12 long, 0.32 broad.

Habitat.—North Pacific (off Japan), Stations 236 to 239, surface.

18. Sethophormis floscula, n. sp.

Cephalis small, hemispherical, with subregular, small hexagonal pores. Thorax flatly conical, with larger hexagonal meshes and twenty-four ribs; four of these are perradial and prolongations of the four collar bars; four interradial arise from the collar ring between the former, alternating with them. Each of these eight main ribs gives off two more or less irregular, lateral branches (one at each side), altogether sixteen. The thorax is similar to Cladarachnium ramosum (Pl. 55, fig. 5), whilst the cephalis is quite different. Peristome with twenty-four prominent triangular lobes.

Dimensions.—Cephalis 0.02 long, 0.03 broad; thorax 0.1 long, 0.4 broad.

Habitat.—South Atlantic, Station 325, surface.

19. Sethophormis leptoscenium, n. sp.

Cephalis very small, spherical, with few small, circular pores. Thorax flatly conical or tent-shaped, with concave lateral outlines, small hexagonal meshes, and numerous (thirty to forty or more) strong, little curved, simple radial ribs. Peristome nearly circular, with a corona of small, irregular, conical spines.

Dimensions.—Cephalis 0.015 diameter; thorax 0.07 long, 0.26 broad.

Habitat.—Indian Ocean, Madagascar (Rabbe), surface.

20. Sethophormis leptopilium, n. sp.

Cephalis very small, subspherical, hyaline, without pores. Thorax flatly conical or hat-shaped, with concave lateral outlines, and a very delicate network of small square meshes (similar to Litharachnium araneosum, Pl. 55, fig. 8). This is supported by thirty-two curved radial ribs, four of which are primary, four secondary, and the other twenty-four interpolated. Peristome horizontally expanded and little recurved, like the reflexed brim of a hat.

Dimensions.—Cephalis 0.12 diameter; thorax 0.08 long, 0.24 broad.

Habitat.—South Pacific, Station 291, depth 2250 fathoms.

Definition.— (vel Dicyrtida multiradiata aperta) with numerous curved ribs in the wall of the ovate thorax, the small mouth of which is constricted. Cephalis without horn.