Page:Scientific results HMS Challenger vol 18 part 2.djvu/45

Rh

Definition.— with three radial spines.

Definition.— with three radial spines, arising from one common central point and lying in one horizontal plane.

The genus Triplecta is the simplest and most primitive of the Plectanida, and may therefore be regarded as the prototype of this family. The skeleton represents a triangular lattice-plate with three radial beams. On the central union of the latter rests the oral pole of the central capsule. Since the axis of the latter is vertical, the lattice-plate must be horizontal, serving for the expansion of the pseudopodia. Triplecta has arisen from Triplagia by union of the branches of its three radial spines. In the simplest case only three large meshes are formed, corresponding probably to the three cortinar meshes in the collar septum of many.

1. Triplecta triangulum, n. sp.

Spines straight, equal, smooth, cylindrical, each in the basal half with one pair of divergent straight lateral branches. The opposed branches of every two neighbouring spines are united by a