Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, surface.
Genus 689. Aulastrum,[[308]] n. gen.
Definition.—Aulosphærida with polygonal meshes in the network, the tangential tubes of which form a simple lattice-sphere. Radial tubes arise at its nodal points.
The genus Aulastrum differs from the preceding Aulonia, its ancestral form, only in the development of radial spines at the nodal points of the simple lattice-sphere. It exhibits therefore to the latter the same relation as Aulosphæra does to Aularia. But the meshes of the spherical network are constantly triangular in the two latter genera, polygonal in the two former. The different species of Aulastrum are much rarer, and are not so differentiated as those of the common Aulosphæra.
1. Aulastrum monoceros, n. sp.
Radial tubes simple, smooth, straight, cylindro-conical, about as long as the smooth tangential tubes or somewhat longer. Meshes of the network irregularly polygonal, the majority usually pentagonal or hexagonal.
Dimensions.—Diameter of the sphere 3.0 to 4.0, of the meshes 0.15; breadth of the tubes 0.012.
Habitat.—Tropical Atlantic, Stations 347, 348, depth 2250 to 2450 fathoms.
2. Aulastrum dichoceros, n. sp.
Radial tubes cylindrical, more or less curved, undulate, smooth, twice as long as the smooth tangential tubes, forked at the distal end, with two divergent curved branches. Meshes of the network subregular, hexagonal (as in Aulonia hexagonia, Pl. [111], fig. 1), intermingled with single pentagonal and square meshes.