Disk with spiny surface, four times as broad as the medullary shell. Pores subregular, circular; fourteen to sixteen on the radius. Equatorial girdle broad, radially striped, on the margin with ten to twelve pyramidal, deeply sulcated radial spines, which are nearly as long as the radius of the disk, and one-fourth as broad at the base.
Dimensions.—Diameter of the disk 0.24, of the medullary shell 0.06; length of the marginal spines 0.11, basal breadth 0.03.
Habitat.—Indian Ocean, between Aden and Ceylon, Haeckel, surface.
Genus 194. Heliodrymus,[[233]] Haeckel, 1881, Prodromus, p. 457.
Definition.—Phacodiscida with simple medullary shell and with numerous (ten to twenty or more) branched radial spines on the margin of the disk (commonly with a variable number and an irregular disposition of the ramified spines).
The genus Heliodrymus differs from the nearly allied Heliodiscus by the ramification of the marginal spines, a character hitherto observed in no other genus of Phacodiscida. The branching is more or less irregular, either a simple bifurcation or a repeated fissure; the spines and their branches are commonly more or less flexuose. We can distinguish two subgenera: in Heliocladus the surface of the disk is smooth, in Heliodendrum covered with bristle-shaped radial spines, which are either simple or also branched, sometimes longer than the thick marginal spines.
Subgenus 1. Heliocladus, Haeckel, 1881, Prodromus, p. 457.
Definition.—Surface of the disk smooth, without radial spines.
1. Heliodrymus dendrocyclus, n. sp. (Pl. [33], fig. 9).
Heliocladus dendrocyclus, Haeckel, 1881, Prodromus et Atlas (pl. xxxiii. fig. 9).