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.
Dimensions.—Diameter of the sphere 2.0 to 2.5, of the meshes 0.12 to 0.18; breadth of the tubes 0.01.
Habitat.—Antarctic Ocean, Station 157, depth 1950 fathoms.
3. Aulastrum dendroceros, n. sp. (Pl. 111, figs. 4a, b, c).
Radial tubes cylindrical, straight or slightly curved, thorny, forked at the distal end, two to three times as long as the thorny tangential tubes; the thorns are short and thin, partly simple, partly irregularly branched and scattered, arborescent. Meshes of the network irregularly polygonal, the majority pentagonal or tetragonal.
Dimensions.—Diameter of the sphere 2.4; radial tubes 0.2 to 0.3 long, 0.02 broad.
Habitat.—North Pacific, Station 241 to 244, surface.
4. Aulastrum triceros, n. sp. (Pl. 111, figs. 3, 3a).
Radial tubes cylindrical, straight, smooth, about twice as long as the smooth tangential tubes, armed with three divergent curved teeth at the distal end. Meshes subregular, pentagonal, intermingled with a small number of tetragonal and hexagonal meshes.
Dimensions.—Diameter of the sphere 1.2 to 1.8; radial tubes 0.15 long, 0.01 broad.
Habitat.—Tropical Atlantic, Station 349, depth 2450 fathoms.
