Page:Scientific results HMS Challenger vol 18 part 2.djvu/756

1632 Dimensions.—Horizontal diameter of the lens 6.0, vertical main axis 1.2; length of the radial tubes 0.2, breadth 0.005.

Habitat.—Indian Ocean, Madagascar (Rabbe), surface.

Definition.— with triangular meshes in the network, the tangential tubes of which form an ellipsoidal or spindle-shaped, simple lattice-shell, with prolonged vertical main axis. Radial tubes arise at its nodal points.

The genus Aulatractus differs from all the other Aulosphærida in the peculiar prolongation of the vertical axis of the lattice-sphere, by which the latter becomes ellipsoidal or spindle-shaped. The triangular meshes of the regular lattice-work become usually more or less irregular and polygonal at the two poles of the elongated main axis. Aulatractus seems to be developed from Aulosphæra in the opposite way from Aulophacus, the former by elongating, the latter by shortening of the vertical main-axis.

1. Aulatractus fusiformis, n. sp. (Pl. 111, figs. 6, 6a, 6b).

Shell spindle-shaped, about twice as long as broad, rounded at both poles of the main axis. Tangential tubes smooth, cylindrical. Radial tubes of the same length as the tangential tubes, but much thinner, slender cylindrical, studded with perpendicularly arising, short, lateral branches, which are scattered in the proximal part, verticillate in the distal part, and bear a spinulate terminal knob.

Dimensions.—Length of the shell 7.5 to 10.0, breadth 3.5; length of the radial tubes 0.15 to 0.18, breadth 0.004.

Habitat.—Tropical Atlantic, Stations 348, 349; surface, and in various depths.

2. Aulatractus diploconus, n. sp. (Pl. 111, fig. 7).

Shell diploconical or nearly spindle-shaped, about three times as long as broad, equally pointed at the two poles of the main axis, not inflated in the middle part. Radial tubes slenderly conical, thorny, only half as long as the smooth tangential tubes.

Dimensions.—Length of the shell 6.0 to 8.0, breadth 2.2 to 4.5; length of the radial tubes 0.1 to 0.15, breadth 0.007.

Habitat.—North Atlantic, Canary Islands, Station 353, surface.

3. Aulatractus fusulus, n. sp.

Shell spindle-shaped, about twice as long as broad, pointed at the two equal poles of the main axis. Radial tubes cylindro-conical, smooth, about as long as the smooth tangential tubes. This