radius, with two widely divergent, conical, curved teeth, a vertical dorsal and a nearly horizontal ventral tooth.
Dimensions.—Diameter of the shell 0.22; length of the peristome 0.1.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
21. Challengeron johannis, n. sp.
Shell ovate, slightly compressed, with a corona of numerous (forty to sixty or more) short radial spines on the margin, ten to fifteen of them (in the aboral half) are pyramidal, and much larger than the others. Peristome helmet-shaped, about one-third as long as the shell, with a deep bosom and two widely divergent teeth on the concave upper margin, a forked dorsal and a conical ventral.
Dimensions.—Length of the shell 0.13, breadth 0.1; length of the peristome 0.04.
Habitat.—North Atlantic, Færöe Channel (Gulf Stream), John Murray.
22. Challengeron carpenterii, John Murray.
Shell ovate, with a series of twelve to fifteen short, conical, radial spines on the aboral half of the margin. Peristome slender, semitubular, nearly as long as the shell, in the upper half forked, with two short parallel teeth.
Dimensions.—Length of the shell 0.13 to 0.18, breadth 0.1 to 0.14; length of the peristome 0.1 to 0.12.
Habitat.—Tropical Atlantic, Stations 347 to 348, depth 2250 to 2450 fathoms.
23. Challengeron ciliatum, n. sp.
Shell ovate, slightly compressed, with numerous (forty to fifty or more) short and thin, bristle-shaped, radial spines on the margin. Peristome obliquely truncate, with three curved spines; the dorsal odd spine subvertical, nearly as long as the radius, and much stronger than the two parallel, nearly horizontal, lateral spines.
Dimensions.—Length of the shell 0.15, breadth 0.11; length of the peristome 0.1.
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,
