1. Prismatium tripodium, n. sp. (Pl. [93], fig. 22).
Mitral ring triangular, somewhat smaller than the triangular basal ring, both connected at the corners by three vertical, slightly curved columellæ. From the six corners arise six radial spines of different size and form; the two paired spines of the mitral ring are simple and very small, whilst those of the basal ring are three times as long and bear a lateral branch. The odd spine of the third corner is on both rings larger, and distinguished by some thorns. This difference seems to indicate that these two odd spines correspond to the apical horn and the caudal foot of Cortina, and the columella between them is the rest of the reduced sagittal ring. In this case the quadrangular vertical ring, which is composed of the two paired columellæ and the two connecting horizontal rods, would be probably the frontal ring.
Dimensions.—Length of the shell 0.09, breadth 0.07.
Habitat.—Equatorial Atlantic, Station 347, surface.
2. Prismatium tripleurum, Haeckel.
Prismatium tripleurum, Haeckel, 1862, Monogr. d. Radiol., p. 270, Taf. iv. fig. 6.
Acanthodesmia prismatium, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 799.
Mitral and basal rings of equal size, equilateral triangular, both connected at the corners by three vertical equal columellæ. From the six corners arise six short, equal, conical radial spines. The nine rods of the shell correspond to the nine edges of a triangular equilateral prism.
Dimensions.—Length of the shell 0.044, breadth 0.032.
Habitat.—Mediterranean (Messina), surface.