Disk with smooth surface, three times as broad as the outer and seven times as broad as the inner medullary shell. Pores subregular, roundish; twelve to fourteen on the radius. Marginal spines one hundred to one hundred and twenty, conical, flexuose, of irregular size and form; the largest one-third as long as the diameter of the disk. The spines lie not only in the equatorial plane (as is usual) but also in two to four crowded girdles on both sides of it. (Very similar to Heliodiscus solaster, Pl. [34], fig. 4, but of double the size, with double the number of spines and with a double medullary shell.)
Dimensions.—Diameter of the disk 0.3, of the outer medullary shell 0.11, of the inner 0.045; length of the spines 0.03 to 0.1, basal breadth 0.01 to 0.02.
Habitat.—Indian Ocean, Sunda Strait, Rabbe, surface.
Subgenus 2. Astrophacilla, Haeckel.
Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.
4. Astrophacus phacodiscus, n. sp. (Pl. [32], fig. 3).
Disk with spiny surface, two and a half times as broad as the outer and seven times as broad as the inner medullary shell. Pores subregular, circular; ten to twelve on the radius. Marginal spines twelve to sixteen, conical, stout, nearly as long as the radius of the disk, and as broad at the base as the inner medullary shell. The numerous bristle-shaped spines of the surface are scarcely half as long. (Similar to Heliodiscus phacodiscus, Haeckel, Monogr. d. Radiol., Taf. xvii. figs. 5-7, but differing in the double medullary shell.)
Dimensions.—Diameter of the disk 0.18, of the outer medullary shell 0.07, of the inner 0.025; length of the marginal spines 0.08 to 0.09, basal breadth 0.03.
Habitat.—South Pacific, Station 300, surface.