Definition.—Spongodiscida with two opposite spongy arms on the margin of the disk, connected by a spongy patagium of different texture.
The genus Spongobrachium differs from the foregoing only in the loose spongy patagium, which envelops both opposite spongy arms. It corresponds to Amphymenium among the Porodiscida and to Amphiactura among the Coccodiscida.
1. Spongobrachium ellipticum, Haeckel.
Spongocyclia elliptica, Haeckel, 1862, Monogr. d. Radiol., p. 470, Taf. xxviii. fig. 2.
Spongodiscus ellipticus, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.
Arms nearly square, scarcely as long and broad as the radius of the circular central disk, at the broader distal end truncated. Patagium complete, enveloping the whole disk with the arms, and forming a larger elliptical disk of looser framework. (In my Monograph, 1862, loc. cit., I had not distinguished the opposite darker arms, opposite in the longer axis of the elliptical disk, from the enveloping looser framework of the patagium. In larger specimens of the Challenger collection this distinction is very evident.)
Dimensions.—Radius of the arms 0.12, breadth 0.05; major axis of the elliptical patagium 0.24, minor 0.16.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.
2. Spongobrachium lanceolatum, n. sp.
Arms club-shaped, twice as long as broad, at the distal end pointed, five times as long as the radius of the circular central disk. Patagium complete, enveloping the whole disk with the arms, and forming a larger lanceolate disk of looser framework. (Similar in form to Amphymenium pupula, Pl. [44], fig. 8, but with an irregular spongy framework and pointed ends.)