1. Challengeron monodon, n. sp.
Shell subspherical, slightly compressed, with a single straight conical spine on the apical pole, about as long as the radius. Peristome with a single vertical, straight, conical tooth, diametrically opposite to the apical spine and of the same length. (Similar to Challengeria naresii.)
Dimensions.—Diameter of the shell 0.2 to 0.3, length of the two opposite spines 0.1 to 0.15.
Habitat.—Central Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms.
2. Challengeron cochlear, n. sp.
Shell nearly circular, lenticular, strongly compressed, with a single straight conical spine on the apical pole, about half as long as the radius. Peristome spoon-shaped, obliquely curved and inclined over the mouth, with a single terminal tooth, somewhat longer than the radius.
Dimensions.—Diameter of the shell 0.1, length of the peristome 0.06.
Habitat.—Indian Ocean, Cocos Islands, Rabbe, surface.
3. Challengeron diodon, n. sp. (Pl. 99, fig. 6).
Shell ovate, slightly compressed, with a single straight conical spine on the aboral pole, half as long as the radius. Peristome short and broad, collar-shaped, about twice as broad as long, and half as long as the radius, obliquely inclined over the mouth, with two divergent straight teeth, which are conical and longer than the shell-radius; beyond each tooth a large ovate hole in the wall of the peristome.
Dimensions.—Diameter of the shell 0.08 to 0.1, length of the teeth 0.06 to 0.08.
Habitat.—South-Eastern Pacific, Station 298, depth 2225 fathoms.
4. Challengeron pearceyi, n. sp. (Pl. 99, fig. 7).
Shell ellipsoidal or subspherical, scarcely compressed, with a single straight conical spine on the apical pole, about as long as the diameter. Peristome slender, semitubular, nearly as long as the diameter, somewhat obliquely inclined over the mouth, with three divergent triangular or lanceolate teeth; the dorsal odd tooth about twice as large as the paired lateral teeth.
Dimensions.—Diameter of the shell 0.08 to 0.12, length of the peristome 0.08 to 0.1.
Habitat.—Antarctic Ocean, between Kerguelen and Heard Island, Station 157.
5. Challengeron swirei, John Murray.
Shell subspherical or somewhat ovate, with a single straight conical spine on the apical pole, about as long as the radius. Peristome slender, semitubular, straight and vertical, nearly as long as the shell, with three pointed teeth, an odd longer terminal and two paired shorter lateral.
Dimensions.—Diameter of the shell 0.06 to 0.08, length of the peristome 0.05 to 0.06.
Habitat.—Antarctic Ocean, Station 157, surface, common.
