Definition.—Peristome with three teeth or trifid, with an odd dorsal and two paired lateral teeth (Challengeriæ triodontes).
14. Challengeria macleari, John Murray.
Challengeria macleari, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 3.
Shell subcircular, lenticular, with a sharp marginal edge. Peristome semitubular, an oblique half-cylinder, with three divergent, short, triangular teeth; the dorsal odd tooth nearly vertical, the paired lateral teeth subhorizontal. Length of the peristome about one-third or one-fourth of the diameter of the shell.
Dimensions.—Diameter of the shell 0.25 to 0.35, length of the peristome 0.1 to 0.12.
Habitat.—South Atlantic, Stations 325 to 332, depth 1715 to 2900 fathoms.
15. Challengeria tridens, n. sp.
Shell subspherical, slightly compressed. Peristome about as long as the radius of the shell, with three diverging and obliquely descending teeth; the dorsal odd tooth twice as long as the paired lateral teeth.
Dimensions.—Diameter of the shell 0.08 to 0.12, length of the peristome 0.05 to 0.07.
Habitat.—North Atlantic, Færöe Channel (Gulf Stream), John Murray.