Disk with smooth surface, three times as broad as the medullary shell. Pores irregular, roundish; eight to ten on the radius. Equatorial girdle half as broad as the medullary shell, hyaline, not radially striped, on the margin with ten to twenty triangular, irregular, smooth teeth, very variable in size and disposition.
Dimensions.—Diameter of the disk 0.15 to 0.2, of the medullary shell 0.05 to 0.06; length of the marginal spines 0.02 to 0.08, basal breadth 0.01 to 0.03.
Habitat.—Cosmopolitan; Atlantic, Pacific, in various depths; also fossil in Barbados and Sicily.
Subgenus 4. Heliodiscura, Haeckel.
Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines connected by a solid equatorial girdle.
19. Heliodiscus apollinis, n. sp.
Disk with spiny or bristly surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius. Equatorial girdle narrow, on the margin with sixteen to twenty broad, flat, triangular teeth, which are half as long and one-fourth as broad as the medullary shell. (Very similar to Astrophacus apollinis, Pl. [32], fig. 2, but with simple medullary shell.)
Dimensions.—Diameter of the disk 0.18, of the medullary shell 0.06; length of the marginal spines 0.03, basal breadth 0.015.
Habitat.—Mediterranean (Corfu), Haeckel, surface.
20. Heliodiscus zoroaster, n. sp.