Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular, very small; twenty-two to twenty-four on the radius of the disk. (The small pores are scarcely half as broad as the thick bars between them.)
Dimensions.—Diameter of the disk 0.25, of the medullary shell 0.06, of the pores 0.002.
Habitat.—South Pacific, Station 288, surface.
4. Sethodiscus lenticula, n. sp. (Pl. [33], figs. 1, 2).
Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, polygonal; eight to nine on the radius of the disk. (The pores of the medullary shell, fig. 2, are also irregular, polygonal, or roundish.)
Dimensions.—Diameter of the disk 0.17, of the medullary shell 0.04, of the pores 0.01.
Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.
5. Sethodiscus macrococcus, n. sp. (Pl. [33], fig. 3).
Disk with smooth surface, two and a half times as broad as the medullary shell. Pores irregular, polygonal; eleven to twelve on the radius of the disk. (The pores of the medullary shell, fig. 3, are regular, circular, with elevated hexagonal frames between them. The figured specimen is a young one, both halves of the biconvex disk being not yet united in the equatorial plane.)
Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.065, of the pores 0.01.