Definition.—Phractopeltida with twelve simple spines (four equatorial and eight polar), and with eight tropical spines protected by external free apophyses.
The genus Octopelta differs from the other Phractopeltida in the possession of eight shields or pairs of free apophyses outside the outer lattice-shell; the spines bearing these apophyses are the eight tropical spines. The twelve other spines (eight polar and four equatorial) are quite simple, without apophyses.
1. Octopelta cultella, n. sp.
Apophyses of the eight tropical spines simple, compressed, knife-shaped, about as long as their distance from the outer shell. On the base of each spine (in the network of the outer shell) two orthogonal aspinal pores, two to three times as long as the other polygonal pores.
Dimensions.—Diameter of the outer shell 0.08, of the inner 0.03.
Habitat.—Tropical Atlantic, Station 338, surface.
2. Octopelta furcella, n. sp.
Apophyses of the eight tropical spines forked, each with two parallel simple fork-branches, about as long as their distance from the outer shell. On the base of each spine (in the outer shell) two kidney-shaped aspinal pores, about twice as broad as the other irregular pores.
Dimensions.—Diameter of the outer shell 0.1, of the inner 0.04.
Habitat.—South Atlantic (off Tristan d'Acunha), Station 332, surface.