Page:Scientific results HMS Challenger vol 18 part 2.djvu/391

Rh outwards. These branches are connected with the spines of the cephalis as well as with the distal half of the ribs, by dense and delicate arachnoidal network, composed of parallel, very thin, siliceous threads (in fig. 11 only partially represented). Collar septum with numerous irregular, roundish pores.

Dimensions.—Cephalis 0.04 diameter, thorax 0.1 long, 0.2 broad.

Habitat.—Central Pacific, Station 270 to 274, surface.

6. Arachnocorys arachnodiscus, n. sp.

Cephalis small, campanulate, conical, with a single very large conical central horn, and numerous smaller accessory spines. Thorax in form and structure similar to that of the three preceding species, but much flatter, being nearly discoidal. The meshes of the network are smaller and more numerous, irregularly polygonal, and the nine basal holes little larger. Collar septum with four large meshes (as in Pl. 60, fig. 6).

Dimensions.—Cephalis 0.25 long, 0.3 broad; thorax 0.04 long, 0.24 broad.

Habitat.—North Pacific, Station 248, surface.

7. Arachnocorys trifida, n. sp.

Cephalis large, campanulate, with irregular, roundish pores and numerous ramified spines; in the centre of the top a larger pyramidal oblique horn of twice the length. Thorax cap-shaped, flatly vaulted, with nine strong convex ribs, prolonged into slender free feet. Three of these nine ribs are the centrifugal prolongations of the three cortinar bars (united in the centre of the collar stricture, separating its three large cortinar meshes); the other six are diverging lateral branches of the former, arising in pairs at both sides of its base. All nine ribs are connected by delicate arachnoidal network with irregular polygonal meshes. From its surface arise thin bristles, and from the base of each main rib a stout, perpendicular branch. All these dorsal spines are connected by irregular, arachnoidal wicker-work, covering thorax and cephalis. (A remarkable primitive species?)

Dimensions.—Cephalis 0.05 long, 0.06 broad; thorax 0.07 long, 0.18 broad.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Definition.—Thorax with a variable number of radial ribs (twelve to twenty or more), prolonged into free terminal feet.

8. Arachnocorys polyptera, n. sp.

Cephalis large, subspherical, with irregular, roundish pores and numerous radial spines. Thorax flatly conical, with numerous radial ribs (twenty to thirty), which are in the distal half free, in the proximal half connected by delicate arachnoidal wicker-work, with polygonal, irregular meshes. From its dorsal face arise numerous radial spines, which are connected together, and with the cephalic spines, by very thin and numerous threads, parallel between every two spines. Similar to