Subgenus 4. Challengerosium, Haeckel.
Definition.—Margin of the shell dentated or serrated, with a continuous series of numerous short radial spines.
17. Challengeron channeri, John Murray.
Shell subcircular, lenticular, strongly compressed, with fourteen to eighteen slender, straight, radial spines on the margin; the spines are straight, equidistant, cylindrical, and about as long as the radius of the shell. Peristome short, with two parallel, vertical, lateral, straight teeth, which are less than half the length of a spine.
Dimensions.—Diameter of the shell 0.14 to 0.17; length of the spines 0.06 to 0.08.
Habitat.—North Pacific, Station 231, depth 2250 fathoms.
18. Challengeron moseleyi, n. sp. (Pl. 99, fig. 14).
Shell circular, lenticular, strongly compressed, with thirty to forty slender, straight, equidistant, radial spines on the margin, larger and smaller spines alternating; the larger spines are about as long as the radius, the smaller only half as long. Peristome short, tubular, with two divergent ovate or nearly triangular teeth, a dorsal and a ventral, about as long as the shorter marginal spines.
Dimensions.—Diameter of the shell 0.13 to 0.15; length of the larger spines 0.06 to 0.07, of the smaller 0.03 to 0.04.
Habitat.—North Pacific, Station 244, depth 2900 fathoms.
19. Challengeron bethelli, John Murray.
Shell subcircular, lenticular, strongly compressed, with numerous (twenty to thirty) short conical spines on the margin (often wanting in the upper part of the dorsal margin). Peristome with a deep labial incision and two parallel triangular lateral teeth, the upper margin of which is horizontal.
Dimensions.—Diameter of the shell 0.2 to 0.25; length of the spines 0.02 to 0.03.
Habitat.—North Pacific, Stations 238, 241 (off Japan), depth between 2300 and 3950 fathoms.
20. Challengeron bathybium, n. sp.
Shell subcircular, lenticular, slightly compressed, with a corona of numerous (thirty to forty or more) short, conical, radial spines on the margin. Peristome helmet-shaped, nearly as long as the
