Habitat.—Fossil in the rocks of Barbados.
8. Histiastrum circulare, n. sp.
Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pl. xxiii. fig. 1.
Arms linear in their inner half, egg-shaped and three times as broad in their outer half, with ten to twelve strong terminal spines, the middle (perradial) larger, in all three times as long as broad. Central disk with three to four rings, broader than their distal knobs. Patagium nearly complete, circular, enveloping the whole arms, with exception of the outermost end.
Dimensions.—Radius of each arm 0.22, basal breadth 0.02, terminal breadth 0.06.
Habitat.—Fossil in the rocks of Barbados; and living in the depths of the Central Pacific, Station 268, depth 2900 fathoms.
9. Histiastrum pentadiscus, n. sp. (Pl. [46], fig. 2).
Arms in their inner half linear, twice as long as broad, in their outer half circular, three times as broad, with the same structure as the central disk, exhibiting three concentric rings around one central chamber. Patagium complete, spongy, with radiating beams, enveloping the whole disk, with the exception of the outermost end of the arms, which is armed with twelve to sixteen strong conical spines, the middle (perradial) spine much larger.
Dimensions.—Radius of each arm (without terminal spine) 0.18, basal breadth 0.025, terminal breadth 0.08.
Habitat.—South Atlantic, Station 333, surface.