Definition.—Peristome with four to six or more teeth.
18. Challengeria quadridens, n. sp.
Shell subglobose, with nearly circular perimeter. Peristome an oblique short and broad tube, the breadth of which is twice as great as its length and equal to the radius of the shell. Margin of the peristome with four divergent, short, triangular teeth, the two dorsal teeth half as long as the two ventral.
Dimensions.—Diameter of the shell 0.22 to 0.24, breadth of the peristome 0.1.
Habitat.—Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms.
19. Challengeria bromleyi, n. sp. (Pl. [99], fig. 3).
Shell ovate, lenticular, strongly compressed. Peristome a broad, trapezoidal, horizontal lamella, the breadth of which is twice as great as its length and nearly equal to the diameter of the shell; its margin with four divergent triangular lamellar teeth, the two dorsal teeth three times as long as the two ventral.
Dimensions.—Length of the shell 0.08 to 0.1, breadth 0.05 to 0.07; breadth of the peristome 0.08.
Habitat.—North Pacific, Stations 244 to 253, surface, and in various depths.
20. Challengeria wildi, n. sp. (Pl. [99], fig. 2).