Page:Scientific results HMS Challenger vol 18 part 2.djvu/755

Rh 2. Auloplegma spongiosum, n. sp. (Pl. 111, fig. 9).

Radial tubes slender, straight, cylindro-conical, studded irregularly with lateral branches, which are short, simple, slightly curved, partly verticillate in the distal third, and ending with a small spinulate knob. The length of the radial tubes is about twice as great as the radial diameter of the spongy framework, which forms the wall of the spherical shell, and is composed of thorny or verticillate cylindrical tubes.

Dimensions.—Diameter of the shell 3.2, of its wall 0.1; length of the radial tubes 0.24, breadth 0.01.

Habitat.—North Pacific, Station 231, surface.

Definition.— with triangular meshes in the network, the tangential tubes of which form a simple, lenticular, biconvex lattice-shell, with shortened vertical main axis. Radial tubes arise at its nodal points.

The genus Aulophacus differs from the common Aulosphæra, its ancestral form, only in the lenticular compression of the spherical lattice-shell, the vertical axis of which is considerably shortened. It exhibits therefore to the latter the same relation as Cenodiscus does to Cenosphæra among the. The contrary condition is shown in the following genus Aulatractus, in which the vertical axis is prolonged. In the two species of Aulophacus observed the radial spines exhibit a remarkable peculiarity, being longer on the circular periphery of the lens, shorter on both its faces, and shortest in the vertical main axis.

1. Aulophacus lenticularis, n. sp. (Pl. 111, fig. 5a).

Shell biconvex, lenticular, with rounded circular margin; its horizontal diameter three times as great as its thickness (or its vertical main axis). Radial tubes cylindro-conical, straight, with six to nine triradiate verticils, those of the margin of the lens twice as long as the smooth tangential tubes, the others shorter.

Dimensions.—Horizontal diameter of the lens 5.5 mm., vertical main axis 0.2; length of the radial tubes 0.2, breadth 0.01.

Habitat.—Indian Ocean, Belligemma, Ceylon (Haeckel), surface.

2. Aulophacus amphidiscus, n. sp. (Pl. 111, fig. 5b).

Shell discoidal, slightly biconvex, with rounded circular margin; its horizontal diameter five times as great as its thickness. Radial tubes cylindrical, covered with numerous short thorns, those of the margin of the lens three times as long as the smooth tangential tubes, the others shorter.