6. Challengeron triodon, n. sp.
Shell ovate, one and a half times as long as broad, not compressed, with a single short and stout conical spine on the apical pole, shorter than half the radius. Peristome short and broad, collar-shaped, nearly half as broad and one-third as long as the shell, with three divergent terminal teeth, an odd dorsal and two paired lateral.
Dimensions.—Length of the shell 0.25 to 0.3, breadth 0.15 to 0.2; length and breadth of the peristome 0.1.
Habitat.—North Pacific, Station 245, surface.
Subgenus 2. Challengerebium, Haeckel.
Definition.—Margin of the shell with two widely distant aboral spines, opposite in the sagittal plane, a dorsal and a ventral.
7. Challengeron balfouri, John Murray.
Shell subcircular, lenticular, strongly compressed, with two short divergent spines on the apical margin (a dorsal and a ventral). Peristome slender, semitubular, as long as the radius, vertical, in the distal half forked, with two parallel teeth.
Dimensions.—Diameter of the shell 0.08 to 0.16, length of the peristome 0.04 to 0.08.
Habitat.—North Atlantic, Stations 353 to 354, Hebrides, surface.
8. Challengeron golfense, n. sp.
Shell ovate, lenticular, compressed, with two short divergent spines on the apical margin (a dorsal and a ventral). Peristome slender, semitubular, half as long as the radius, with three terminal teeth, two short, vertically ascending, paired teeth and a larger odd tooth, which is inclined obliquely over the mouth.
Dimensions.—Diameter of the shell 0.15 to 0.2, peristome 0.05 to 0.07.
Habitat.—North Atlantic, Færöe Channel, Gulf Stream, surface and at various depths, John Murray.
9. Challengeron richardsii, n. sp. (Pl. 99, fig. 8).
Shell subcircular, lenticular, strongly compressed, with two stout, divergent, straight spines on the aboral margin (a dorsal and a ventral) which reach the length of the radius. Peristome slender, semitubular, slightly curved, about as long as the radius, with three short, divergent,
