Habitat.—Central Pacific, Station 267, surface.
Subfamily 2. Tetraplectida, Haeckel, 1881, Prodromus, p. 424.
Definition.—Plectanida with four radial spines.
Genus 395. Tetraplecta,[[14]] Haeckel, 1881, Prodromus, p. 424.
Definition.—Plectanida with four equal radial spines, arising from one common central point and corresponding to the four axes of a tetrahedron.
The genus Tetraplecta has been derived from Tetraplagia by union of the neighbouring branches of the four radial spines, diverging from a common point in different directions. In some forms of this genus the four rods seem to correspond exactly to the four axes, which are directed from the centre of a tetrahedron towards its four corners; whilst in other forms the four rods and the angles between them are perhaps not perfectly equal.
1. Tetraplecta tetrahedra, n. sp.
Spines straight, equal, three-sided prismatic, pinnate, each with three or four pairs of opposite straight slender pinnulæ or lateral branches; the pinnulæ of each side are correspondingly parallel. All pinnulæ connected by a few slender bridges, thus producing a delicate network with irregular rhomboidal meshes.
Dimensions.—Length of the spines 0.15, of the basal branches 0.05.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.