13. Challengeron bisternum, n. sp.
Shell subcircular, lenticular, strongly compressed, with three stout conical spines on the aboral pole; the middle spine is placed in the main axis, as long as the radius and three times as long as the two others. Peristome semitubular, straight, vertical, about as long as the radius, with three divergent teeth, the middle of which is odd and twice as large as the two paired lateral teeth.
Dimensions.—Diameter of the shell 0.22; length of the peristome 0.1.
Habitat.—Indian Ocean, Madagascar (Rabbe), surface.
14. Challengeron heptacanthum, n. sp.
Shell ovate, slightly compressed, with a series of five stout, conical, radial spines on the aboral margin; the middle spine is placed in the main axis and longer than the radius, twice as long as the two next, and three times as long as the more distant spines. Peristome short and broad, collar-shaped, with two large, divergent, straight teeth, each of which is longer than the shell-radius and bears at its base a large hole.
Dimensions.—Length of the shell 0.09 to 0.11, breadth 0.07 to 0.08; length of the teeth 0.07.
Habitat.—Tropical Atlantic, Stations 347, 348, depth 2250 and 2450 fathoms.
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.
