1656 THE VOYAGE OF H.M.S. CHALLENGER. 



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 01. 



Habitat. Western Tropical Pacific, Station 224, depth 1850 fathoms. 



11. Challengeron tizardi, John Murray. 



Challengeria tizardi, John Murray, 1879, in litteria, Narr. Chall. Exp., vol. i. p. 226, pi. A, 

 figs. 7-76. 



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 O'Ol to 012. 



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 ventra 

 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 01 to 012. 



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. 



