terminal teeth. Mouth obliquely truncate. The dorsal odd tooth is nearly vertical, the two lateral paired teeth almost horizontal.
Dimensions.—Diameter of the shell 0.2 to 0.25, length of the spines and the peristome 0.08 to 0.12.
Habitat.—Antarctic Ocean, Station 157, surface, common.
10. Challengeron fergusoni, n. sp. (Pl. 99, fig. 9).
Shell isosceles triangular, with three slightly convex edges and two short, nearly vertically descending spines on the two corners of the aboral margin. Peristome inversely funnel-shaped, with a deep ventral incision on the base, and three broad, ovate, triangular teeth. The dorsal odd tooth is nearly vertical, whilst the two lateral paired teeth are almost horizontal; therefore the angle between the former and the latter is about a right angle.
Dimensions.—Diameter of the shell 0.2 to 0.3, length of the peristome 0.1.
Habitat.—Western Tropical Pacific, Station 224, depth 1850 fathoms.
11. Challengeron tizardi, John Murray.
Shell nearly equilateral triangular, with concave ventral, convex dorsal and aboral edges, on the two corners of the latter two opposite horizontal spines (a dorsal and a ventral). Peristome auriculate and bilobate, with a deep ventral incision on the base, and three pointed triangular teeth, the upper margins of which are nearly horizontal.
Dimensions.—Diameter of the shell 0.22 to 0.3, length and breadth of the peristome 0.01 to 0.12.
Habitat.—South Atlantic, Stations 332 to 335, depth 1425 to 2200 fathoms.
12. Challengeron triangulum, n. sp. (Pl. 99, fig. 10).
Shell nearly equilateral triangular, with three slightly convex or nearly straight sides, and two opposite obliquely descending and diverging spines on the two corners of the aboral margin. Peristome auriculate and bilobate, with a very thin basal neck and a deep incision on its ventral side; its distal margin is obliquely truncate, and exhibits an odd ascending dorsal tooth and two parallel, paired, descending, lateral teeth.
Dimensions.—Diameter of the shell 0.2 to 0.3; length and breadth of the peristome 0.1 to 0.12.
Habitat.—North Pacific, Stations 244 to 253, depth 2050 to 3125 fathoms.
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.
