Page:Scientific results HMS Challenger vol 18 part 2.djvu/368

1244 2. Sethophormis medusa, n. sp.

Cephalis very large, flat, cap-shaped, with irregular, delicate network of polygonal meshes. Thorax flat, campanulate, nearly hemispherical, with delicate, irregular network of small polygonal meshes. All bars very thin, thread-like. Four stout radial thoracic ribs, as in the preceding species. Peristome denticulate.

Dimensions.—Cephalis 0.03 long, 0.09 broad; thorax 0.15 long, 0.25 broad.

Habitat.—North Pacific, Station 244, surface.

Definition.—Thorax with five radial ribs, one of the three primary ribs (the odd occipital rib) being simple, the two others (the paired lateral ribs) forked.

3. Sethophormis pentalactis, n. sp. (Pl. 56, fig. 5).

Cephalis large, flat, hemispherical, with subregular, hexagonal pores. Thorax flat, campanulate, nearly hemispherical; also with subregular, hexagonal pores, and with five stout ribs. The three primary ribs of the thorax are complete, and reach the peristome; the two secondary ribs (as basal branches of the two lateral ribs) are incomplete and absent in the distal half of the thorax. Peristome denticulate, with an elegant marginal corona of small square pores and short conical spines.

Dimensions.—Cephalis 0.03 long, 0.06 broad; thorax 0.1 long, 0.2 broad.

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

4. Sethophormis asteriscus, n. sp.

Cephalis large, flat, cap-shaped, with irregular polygonal pores. Thorax flat, campanulate, with subregular, hexagonal pores, and five stout ribs. The marginal distance between the two anterior (lateral) ribs is twice as great as the distance between every two other ribs (the postero-lateral ribs being basal branches of the antero-lateral ribs). Peristome with a double corona of short, conical spines.

Dimensions.—Cephalis 0.02 long, 0.04 broad; thorax 0.06 long, 0.17 broad.

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

5. Sethophormis astrodiscus, n. sp.

Cephalis small, flatly vaulted, cap-shaped with irregular polygonal pores. Thorax very flatly vaulted, nearly discoidal, with subregular hexagonal pores, and five stout ribs. The marginal distance between all five ribs is nearly equal. Peristome denticulate with an elegant corona of small square pores and short conical thorns.

Dimensions.—Cephalis 0.015 long, 0.035 broad; thorax 0.05 long, 0.2 broad.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.