1648 THE VOYAGE OF H.M.S. CHALLENGER. 



Genus 694. Challengeria, John Murray, 1876, Proc. Roy. Soc. Lond., 



vol. xxiv. p. 536. 



Definition. Challenger id a without pharynx, with one or more adoral teeth, 

 but without spines on the sagittal margin. 



The genus Challengeria, and the following closely allied Challenger on, differ from 

 the preceding Lithogromia, their ancestral form, in the development of teeth on the 

 mouth of the shell. Challengeron has also radial spines on the sagittal margin, while 

 these are wanting in Challengeria. The latter genus exhibits not less than twenty-one, 

 the former twenty-five species, so that both together make by far the greatest part of 

 the family (containing fifty-eight species). They are also more common and more widely 

 distributed than the four other genera of Challengerida, and many species appear in 

 great numbers in certain localities. With a few exceptions living on the surface, they 

 are all inhabitants of great depths. 



Subgenus 1. Challengerantha, Haeckel. 



Definition. Peristome with a single simple tooth, which is neither forked nor 

 branched (Challengerice monodontes). 



1. Challengeria naresii, John Murray. 



Challengeria naresii, John Murray, 1876, Proe. Roy. Soc. Lond., vol. xxiv. pi. xxiv. fig. 1. 

 Challengeria naresii, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 236, pi. A, 

 figs. 1, la-le. 



Shell circular or nearly circular, strongly compressed, lenticular. Peristome on the dorsal 

 corner with a single simple vertical tooth, which is nearly straight, conical, with two sharp lateral 

 edges on the base, about half as long as the shell. 



Dimensions. Diameter of the shell O5 to 0'6, length of the tooth 0'2 to 0'3. 



Habitat. Cosmopolitan ; Atlantic, Indian, Pacific, at depths between 1000 and 3000 fathoms. 



2. Challengeria xiphodon, n. sp. 



Shell circular, nearly spherical, slightly compressed. Peristome on the dorsal corner with a 

 single simple vertical tooth, which is straight, three-sided prismatic, and as long as the shell. 

 Dimensions. Diameter of the shell 01 to 013, length of the tooth 01 to 012. 

 Habitat. Tropical Atlantic, Stations 349 to 352, surface. 



