Habitat.—North Pacific, Station 231, depth 2250 fathoms.
24. Challengeron willemoesii, n. sp. (Pl. [99], fig. 13).
Shell broadly-ovate or nearly circular, lenticular, with numerous (fifty to sixty) short and stout, conical, radial spines on the margin, increasing in size towards the aboral pole; the spines are alternately larger and smaller, the largest about half as long as the radius. Peristome helmet-shaped or half conical, longer than the radius of the shell, with two pairs of conical, curved, divergent teeth; the terminal teeth are the halves of a forked dorsal tooth and diverge laterally; the lower teeth are nearly horizontal and directed ventrally.
Dimensions.—Diameter of the shell 0.13 to 0.15; length of the peristome 0.07 to 0.1.
Habitat.—Tropical Pacific, Stations 274 to 276, depth 2350 to 2750 fathoms.
25. Challengeron wyvillei, n. sp. (Pl. [99], fig. 15).
Shell ovate, lenticular, strongly compressed, with numerous (forty to fifty) short, conical, radial spines on the margin; the spines are larger on the aboral side and spinulate. Peristome narrow, with two parallel, lateral, lamellar, forked teeth, about as long as the radius; the upper branch of the forks is sabre-shaped, obliquely truncate, subvertical, ciliate, and much broader than the lower nearly horizontal branch, which is directed towards the ventral side and curved upwards.
Dimensions.—Length of the shell 0.12 to 0.16, breadth 0.1 to 0.14; length of the peristome 0.08 to 0.11.
Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.