Page:Scientific results HMS Challenger vol 18 part 2.djvu/874

1750 branches of different lengths; the anterior (or pectoral branch) twice as long (in the free part) as the diameter of the fork-thicket, the posterior (or tergal branch) three times as long.

Dimensions.—Diameter of the whole body 20, of the fork-thicket 3.2.

Habitat.—Indian Ocean (Sunda Strait), Rabbe, surface.

Definition.— with two paired lateral frenula on each galea, without external lattice-mantle, armed with twelve styles (three pairs of styles on each valve).

The genus Cœlothauma differs from the preceding Cœlotholus, its ancestral form, in the possession of twelve long, prominent styles, six of which are opposite in three pairs on each valve. In the single species observed each of the four main tubes (opposite in pairs on the frontal corners of the two galeæ) is simply forked, as in Cœlotholus; but whilst in this latter all eight styles remain simple, in Cœlothauma the anterior (or pectoral) branch only is simple, the posterior (or tergal) branch is again forked.

1. Cœlothauma duodenum., n. sp. (Pl. 122, figs. 3-5).

Twelve styles straight, of different lengths. Two short bilateral main tubes arise opposite in pairs from the two frontal corners of each galea, and are divided into an anterior and posterior branch. The anterior or pectoral branch is simple, and twice as long as the diameter of the fork-thicket. The posterior or tergal branch is again forked near the base, and its two divergent branches are three times as long as the diameter of the fork-thicket. All twelve styles are densely studded with anchor-pencils of nearly equal size.

Dimensions.—Diameter of the whole body 21, of the fork thicket 3.5.

Habitat.—South-Western Pacific (east of New Zealand), Station 169, depth 700 fathoms.

Definition.— with two paired lateral frenula on each galea, without external lattice-mantle, armed with sixteen styles (four pairs of styles on each valve).

The genus differs from its ancestral form, Cœlotholus, in the duplication of the number of long verticillate styles, which are prominent over the surface of the