Page:Scientific results HMS Challenger vol 18 part 2.djvu/757

Rh species resembles in its simple structure the common cosmopolitan Aulosphæra trigonopa, and differs from it only in the constant spindle-form of the shell.

Dimensions.—Length of the shell 6 to 8, breadth 3 to 4; length of the radial tubes 0.16 to 0.2, breadth 0.008.

Habitat.—North Atlantic, Færöe Channel, Gulf Stream (John Murray); Hebrides (Mœbius).

4. Aulatractus ellipsoides, n. sp.

Shell ellipsoidal, about twice as long as broad, with equally rounded poles on the main axis. Radial tubes straight, cylindrical, verticillate, about twice as long as the smooth tangential bars; each verticil is cruciate, composed of four rectangularly crossed, short, lateral branches which bear a small spathilla at the distal end.

Dimensions.—Length of the shell 6.6, breadth 3.6; length of the radial tubes 0.2, breadth 0.01.

Habitat.—South Atlantic, Station 332, surface.

Definition.—Network of the shell with polygonal, usually irregular meshes; three or four tangential tubes usually being united at each nodal point.

Definition.— with polygonal meshes in the network, the tangential tubes of which form a simple smooth lattice-sphere. No radial tubes at the nodal points.

The genus Aulonia is the simplest form of the subfamily Aulonida, or of those Aulosphærida in which the lattice-work of the shell is composed not of triangular but of polygonal meshes; all these Aulonida are much rarer and much less differentiated than the Aularida or the common Aulosphærida with triangular meshes. Aulonia has the same simple, smooth, spherical lattice-shell as Aularia, and differs from it only in the polygonal form of the meshes, which, however, is very constant.

1. Aulonia tetragonia, n. sp.

Meshes regular or subregular, square, sometimes intermingled with a variable number of irregular, triangular, and pentagonal meshes. Bars cylindrical, of equal breadth.

Dimensions.—Diameter of the spherical shell 2.0 to 3.2, of the meshes 0.12 to 0.18; breadth of the bars 0.008.

Habitat.—Antarctic Ocean, Station 154, depth 1800 fathoms.