368 BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



Genus ONYCHOMYS Baird (18B7).« 



Onychomys Baird, Mam. N. Am., 1857, p. 457 (subgenus). — ^Merriam, North Ameri- 

 can Fauna, No. 2, 1889, p. 3, text figs. 1 and 2 (raised to generic rank). 



Dentition.— l.'^^] M.t? = 16. 



Type — Hypudseus leucogaster Max. zu Wied.* 



Similar to Per(?mi/scus, except as follows : Body stout; pelage dense; 

 tail short, thick, and usually all white at the end; ears small and 

 hairy; fore feet large; hind feet with only four tubercles, all phalan- 

 geal; nasal bones wedge-shaped, ending, posteriorly, well behind the 

 nasal processes of the premaxillaries; coronoid process of mandible 

 developed as a long hook; dentition heavy, but with last upper molar 

 disproportionately small; dental tubercles high; most closely allied 

 to the subgenus Trinodontomys of Peromyscus. 



The seven forms of the genus Onychomys known to inhabit the 

 Mexican Border may be considered as forming- two groups, one con- 

 taining three large forms, which resemble 0. leucogaster, the other 

 four small forms resembling 0. torridus. Hence they may be conven- 

 iently designated, respectively, the leucogaster group, and the torridus 

 group. The four components of the latter are distributed continu- 

 ously from near the Pecos River, Texas, to the Pacific Ocean, the 

 former having an interrupted distribution between the Gulf of Mexico 

 and the Santa Cruz Valley, of Arizona and Sonora. The four mem- 

 bers of the torridus group are known to be intergrading geographical 

 races of a common species; but the relationship of the three mem- 

 bers of the leucogaster group to each other and to 0. leucogaster are 

 not plain, because the three are separated by considerable areas in 

 which no specimens have been taken, and no specimens exhibiting 

 intermediate characters have yet been recorded. It seems to be 

 desirable, therefore, at present to consider the three larger forms as 

 species. The four small forms are evidently subspecies of Ony- 

 cTiomys torridus Coues. 



a Of all our murine genera, Onychomys is preeminently carnivorous and largely insectiv- 

 orous; hence the appropriateness of the names grasshopper mice and scorpion mice, which 

 have obtained a foothold in vernacular nomenclature of late. The name grasshopper mice, 

 by usage, and because of its general applicability, is to be preferred. Dr. Elliott Coues, in 

 the monographs of Rodentia, has styled the members of this genus mole-mice, a not inap- 

 propriate name, which the dense pelage, short, thick tail, and strongly developed feet of 

 these animals may have suggested; but the name mole-rat, having long been in use for cer- 

 tain Old World rodents, naming our Onychomys mole-mice might lead to contusion. 



*Reise das innere Nord Amerika, II, 1841, pp. 99-101 (from Fort Clark, Dakota). 



