Page:Scientific results HMS Challenger vol 18 part 2.djvu/858

1734 The genus Cœlodoras is the simplest form of the Cœlodendrida, and may be regarded as the common ancestral form of this and of the following family. It differs from all other members of these two families in the simple shape of the hollow radial tubes which arise from the galea, and are neither branched nor forked; the galea is very small, a flat triangular cap. Cœlodoras may be derived immediately from Concharium or Conchonia (p. 1723), by development of the galea and the radial tubes.

1. Cœlodoras hexagraphis, n. sp.

Three straight, cylindrical, equidistant hollow tubes arise divergent from the three corners of each galea, and are about as long as the diameter of the valves, at the distal end armed with a spinulate knob. The odd sagittal (or caudal tube) is directed backwards, the two paired (or pectoral) tubes, forwards.

Dimensions.—Diameter of the valves 0.16, length of the tubes 0.2.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Cœlodoras octographis, n. sp.

Four hollow cylindrical tubes, slightly curved, arise divergent from each galea, and are about one and a half times as long as the diameter of the valves, at the distal end knob-shaped, and armed with four crossed, recurved teeth. Two anterior (or pectoral) tubes arise from the two frontal corners of the galea basis, and diverge forwards to right and left. Two posterior tubes (a sagittal and a caudal) arise from the posterior corner of each galea, and diverge in the sagittal plane backwards.

Dimensions.—Diameter of the valves 0.2, length of the tubes 0.3.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

Definition.— without external lattice-mantle, with branched radial tubes, the hollow branches of which are free and never connected by anastomoses.

The genus Cœlodendrum is the first described form not only of the family Cœlodendrida, but of all or bivalved ; it is also the most common form of this group, and represented by ten different species, some of which are cosmopolitan, very common, and widely distributed. In my first description of Cœlodendrum I confounded it erroneously with some forms of Cœlodasea and Cœlographis, the separated fragments of which I had found entangled between the branches of the former. The first figures of Cœlodendrum are given in my Monograph, in 1862,