Page:Scientific results HMS Challenger vol 18 part 2.djvu/51

Rh 3. Periplecta monocyrtis, n. sp.

Spines of nearly equal size and shape, cylindrical, irregularly branched. The apical spine is straight, more branched and nearly twice as long as the three basal spines. All four spines in the basal third connected by a loose spongy framework, approaching the form of some Monocyrtida.

Dimensions.—Length of the apical spine 0.24, of the basal spines 0.13.

Habitat.—Central Pacific, Station 274, surface.

Definition.— with six radial spines.

Definition.— with six radial spines, arising from one common central point.

The genus Hexaplecta has probably been derived from Hexaplagia by concrescence of the meeting branches of the six spines, and therefore has to it the same relation that Plectophora bears to Plagiacantha. The two species here described represent perhaps two different genera, since in the first all six spines are equal, opposed in pairs, in the second different in pairs (three upper smaller and three lower larger).

1. Hexaplecta triaxonia, n. sp.

Spines equal, opposite in three crossed pairs, straight, three-sided prismatic, thorny, in the distal half with three leaf-shaped, dentate edges, in the basal half with three verticils of slender branches, which are connected by parallel threads, and so form an arachnoidal network with rectangular or rhomboidal meshes.

Dimensions.—Length of the spines 0.22, of their basal branches 0.06.

Habitat.—South Pacific, Station 285, depth 2375 fathoms.

2. Hexaplecta tricladonia, n. sp.

Spines unequal, three larger spines (in the lower half of the body) being opposite to three smaller spines (in the upper half). The latter are nearly horizontally expanded, each bearing three straight divergent branches. The larger are stronger, twice as long and armed with three verticils, each of three branches. All six spines are slender, three-sided prismatic. Their branches are very thin, thread-shaped, and form by their union a loose network with irregular polygonal meshes.

Dimensions.—Length of the larger spines 0.25, of the smaller 0.12.

Habitat.—South Pacific, Station 291, surface.