15. Challengeron crosbiei, n. sp. (Pl. [99], fig. 11).
Shell ovate, strongly compressed, with a series of seven to nine conical spines on the aboral margin; the middle spine is placed in the main axis, as long as the radius, and much larger than the six or eight other spines. Peristome short and broad, collar-like, with several small spines and two slender, widely distant, conical teeth, which are half as long as the shell, and curved towards one another like a pincer, each with a large hole at its base.
Dimensions.—Length of the shell 0.08 to 0.09, breadth 0.06 to 0.07; length of the two larger teeth 0.04 to 0.05.
Habitat.—Central Pacific, Station 270 to 274, depth 2350 to 2925 fathoms.
16. Challengeron buchanani, n. sp. (Pl. [99], fig. 12).
Shell ovate, slightly compressed, with a terminal comb of nine to twelve conical radial spines, densely crowded on the aboral pole; the middle spine is placed in the main axis, about half as long as the shell and much larger than the others. Peristome subconical, semitubular, recurved, half as long as the shell, with five triangular teeth; the dorsal odd tooth is inclined backwards, the two parallel pairs of lateral teeth directed ventrally.
Dimensions.—Length of the shell 0.15 to 0.18, breadth 0.1 to 0.12; length of the peristome 0.06 to 0.08.
Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.
Subgenus 4. Challengerosium, Haeckel.
Definition.—Margin of the shell dentated or serrated, with a continuous series of numerous short radial spines.