182 PROCEEDINGS OF THE ACADEMY OF 



Ohs. This may just possibly be H. mexicanus of De Saussure, 

 but I cannot so identify it, and prefer to err on the safe side, if at 

 all. Besides tiie above specimen, I have others from Tehuacan 

 and Tehuantepec. It is nothing like any of the foregoing North 

 American species. A female shows three pair of mammae one 

 axillary, two inguinal. 



Subgenus Onychomys, Baird. 



Syn. irypud(PACs, sp., Maxim., Reise, ii. 1841, 99, nee cmct. Mus, sp., Aud. 

 & Bach., Q. N. A. ii. 1851, 327 {missoiin'eiisis), HeKperomys subg. 

 Onydiomys^ Baird, M. N. A. 1857, 458 (tj'pe Hypudmus leucogaster, 

 Maxim.). 



Diag. Skull strictly' as in Hesperomys (Vesperimus), but mo- 

 lars larger with sharper saliencies and re-entrances. Coronoid 

 attaining level of condyle. External form somewhat approaching 

 the arvicoline in stoutness, and in shortness of tail and ears. 

 Tail in tj-pe of the genus not one-half the length of the bod}' 

 alone little if any longer than the head, very thick and tapering 

 to an obtuse point. Ears about as in the arvicoline genus Evoto- 

 mys (Hypudseus of Baird). Fore feet very large, f to ^ as long 

 as the hinder, with long, little curved, almost fossorial claws, 

 longer than those of the hind feet. Soles quadrituberculate only 

 densely furry to the tubercles. White beneath, as in typical 

 Vespe7-imus. A strongly differentiated form ! To the type of this 

 section (Hypudseus leucogaster of Maximilian, afterward Mus 

 missouriensis of Audubon) I add a peculiar variety more proba- 

 bly a second species. The two may be thus distinguished: 



a. Tail much less than half the head aud body, scarcely twice the hind foot. 

 Fore foot more than half the liiud foot. Ear about 0.50 high. Be- 

 neath snow-white ; above mouse -browu with darker dorsal area. 



LEUCOGASTEK. 



h. Tail nearly half the head and body, about 3| times the hind foot. Fore 

 foot only half the hind foot. Ear about 0.75 high; beneath tawny 

 white ; above brownish fulvous without darker dorsal area. 



(var ?) TORRIDUS. 

 7. Hesperomys (Onycliomys) leucogaster, (Maxim.) Baird. 

 Syn. Hypudaus leucogaster, Maxim., Reise, ii. 1841, 99 (Fort Clark). 

 Hefiperomys {Onycliomys) leucogaster, Bd., M. N. A. 1857, 480. 

 (Nebraska.) 



Mus missouriensis, Aud. & Bach., Q. N. A. ii. 1851, 327, pi. 100. 

 (Fort Union, Montana.) 



