Page:Scientific results HMS Challenger vol 18 part 2.djvu/370

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Definition.—Thorax with nine radial ribs, three of which are the primary beams, the other six being secondary and interpolated.

9. Sethophormis rotula, n. sp. (Pl. 57, fig. 9).

Enneaphormis rotula, Haeckel, 1881, Prodromus et Atlas, pl. lvii. fig. 9.

Cephalis very large, flat, cap-shaped, trilobed, with irregular, polygonal network. Horizontal collar-ring stout, hexagonal, with three larger and three alternate smaller sides of half the length. From the middle of the three larger sides arise three horizontal, centripetal, radial beams, which are united in the centre of the collar-septum—the three primary cortinar beams. These are prolonged outside into three centrifugal primary ribs of the thorax. From the six corners of the collar-ring arise six other secondary, thoracic ribs, equal in size and similar in form to the three primary. Each of these nine equal, straight ribs of the thorax is thickened towards the distal end, and bears at equal distances five pairs of opposite (tangential) lateral branches. The opposite branches of the neighbouring spines become united, and lie nearly horizontally in one plane, so that the flat, discoidal thorax is like a nine-angled wheel with nine equally distant spokes and five concentric, nine-angled rings.

Dimensions.—Cephalis 0.12 diameter, thorax 0.36 diameter.

Habitat.—Central Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms.

10. Sethophormis triloba, n. sp.

Cephalis large, hemispherical, distinctly trilobed, with dense, irregular, polygonal network. From the centre of its top diverge three stout arches or semilunar rods, which are curved downwards, and unite with the three horizontal, radial beams of the collar-septum inside the collar-ring. These three parietal arches of the cephalis are much stronger than in the similar preceding species (Pl. 57, fig. 9), and between them are placed three vaulted bosoms of the cephalis. The collar-ring and the thorax are of the same form as in the preceding, but possess only four concentric, nine-angled rings.

Dimensions.—Cephalis 0.05 long, 0.08 broad; thorax 0.24 diameter.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

11. Sethophormis enneastrum, n. sp.

Cephalis very large, flat, cap-shaped, with hexagonal base, trilobed, of similar form and structure to the two preceding species. The flat, discoidal thorax has also the same form, with nine stout ribs and five concentric, nine-angled rings; its forty-five large meshes, however, are not so simple