Dimensions.—Radius of the arms 0.16, breadth 0.05; major axis of the lanceolate patagium 0.32, minor axis 0.12.
Habitat.—Pacific, central area, Station 270, surface.
Genus 262. Rhopalodictyum,[[301]] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 830.
Definition.—Spongodiscida with three spongy arms on the margin of the circular or triangular disk, without a connecting patagium.
The genus Rhopalodictyum comprises those very common forms of Spongodiscida in which the margin of the disk is provided with three simple, free, spongy arms. It corresponds to Dictyastrum and Rhopalastrum among the Porodiscida, to Trigonactura among the Coccodiscida. The typical species of this genus is Rhopalodictyum abyssorum of Ehrenberg, the only species figured by him. His diagnosis of the genus was very insufficient, and agreed with that of his Dictyastrum (compare above the improved diagnosis of this genus, p. [526], and my Monograph, p. 466).
Subgenus 1. Rhopalodictya, Haeckel.
Definition.—Triangular shell regular, with three arms of equal size and equidistant.
1. Rhopalodictyum abyssorum, Ehrenberg.
Rhopalodictyum abyssorum, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. viii. fig. 17.
Arms of equal size and equidistant, club-shaped, about as long as the diameter of the triangular central disk, and a little longer than the breadth of the pear-shaped rounded distal end. Surface rough.