Page:Scientific results HMS Challenger vol 18 part 2.djvu/389

Rh third are separated by the same number of large, triangular meshes, in the middle third connected by irregular network, in the distal third free.

Dimensions.—Cephalis 0.02 long, 0.03 broad; thorax 0.06 long, 0.15 broad.

Habitat.—Central Pacific, Station 273, depth 2350 fathoms.

Definition.— (vel Dicyrtida multiradiata aperta) with numerous radial ribs in the wall of the pyramidal thorax, prolonged into divergent terminal feet. Network double, with an arachnoidal outer mantle around the inner lattice-shell. Cephalis commonly with numerous horns.

The genus Arachnocorys has been derived from the preceding Acanthocorys, by development of numerous external siliceous threads which connect the radial horns of the cephalis with the secondary spines arising from the thoracic ribs. In this way there becomes formed an outer arachnoidal framework, enveloping loosely, like a delicate mantle, the inner primary lattice-shell.

Definition.—Thorax with six divergent ribs or radial beams (three primary or perradial, alternating with three secondary or interradial).

1. Arachnocorys hexaptera, n. sp.

Arachnocorys circumtexta (juv.?), R. Hertwig, 1879, Organism. d. Radiol., p. 79, Taf. viii. fig. 2a.

Cephalis large, subspherical, with irregular, polygonal pores, and numerous bristle-shaped spines twice the length; on the centre of the top a single larger vertical horn. Thorax flatly conical, with six strong and straight widely divergent ribs, which in the proximal half are separated by six large holes, in the distal half connected by a broad ring of irregular network. From each rib arises a perpendicular branch, and these branches are connected together, and with the spines of the cephalis, by arachnoidal network.

Dimensions.—Cephalis 0.04 diameter, thorax 0.08 long, 0.24 broad.

Habitat.—Central Pacific, Station 266; Mediterranean, surface.

2. Arachnocorys discoides, n. sp.

Cephalis small, pyramidal, with irregular, roundish pores and numerous thin spines, on the top a single larger vertical horn. Thorax very flat, nearly discoidal, with six strong and straight ribs,