Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.
1. Astrophacus asteriscus, n. sp.
Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; twelve to fourteen on the radius. Marginal spines fifteen to twenty, of variable size and disposition; the largest as long as the radius of the disk, as broad at the base as one pore. (Very similar to Heliodiscus asteriscus, Pl. [33], fig. 8, but differing in the double medullary shell.)
Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.025; length of the marginal spines 0.05 to 0.1, basal breadth 0.01.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
2. Astrophacus trochiscus, n. sp. (Pl. [34], fig. 14).
Disk with smooth surface, three times as broad as the outer and seven times as broad as the inner medullary shell. Pores irregular, roundish; twelve to thirteen on the radius. Marginal spines sixteen to twenty, conical, of irregular variable size and disposition; the largest as long as the inner medullary shell. (Differs from Heliodiscus trochiscus in the double medullary shell.)
Dimensions.—Diameter of the disk 0.22, of the outer medullary shell 0.08, of the inner 0.03.
Habitat.—North Atlantic, Station 354, surface.
3. Astrophacus solaris, n. sp. (Pl. [32], fig. 1).