Subgenus 3. Challengeridium, Haeckel.
Definition.—Margin of the shell smooth on the dorsal and the ventral side, but with three to five or more large spines (or a bunch of spines) on the aboral side; the middle spine is placed in the main axis, and larger than the others.
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.