110 MONOGRAMS OF NORTH AMERICAN RODKNTIA. 



larger. This is particularly noticeable in the ears. The small arvicola-Iike 

 ears of O. leucogaster arc among its striking external features; in torridus, the 

 ears are fully as long as in ordinary Hesperomys, measuring nearly three- 

 fourths of an inch long by about half an inch wide. The ears are delicately 

 pilous, with fluffy tuft at base; basally, the membrane is flesh-colored, other- 

 wise it is dusky, with a delicate silvery margin. The fore feet-have the claws 

 noticeably smaller than in average leucogaster, but this is a very variable fea- 

 ture iu the latter species. It is probably owing to this shortness of the claws 

 that in torridus the hands are only half as long as the soles; in leucogaster, 

 they are almost invariably more than this; sometimes upward of two-thirds 

 as long. The hind feet are pilous underneath to the toes, showing only four 

 tubercles, as in leucogaster, but the hairiness is not so dense. The tail, like 

 the ears, is much longer than in leucogaster. In the latter, it ordinarily ranges 

 from 1J to 1§ of an inch in length, sometimes scarcely exceeding the length 

 of the head, and being usually less than twice the hind foot. In torridus, the 

 tail is at least half the head and body together, and noticeably more than 

 twice as long as the hind foot. These various discrepancies in form are, in 

 fact, so prominent that we have been obliged to remodel in some respects 

 the diagnosis of the subgenus, as we originally drew it up from consideration 

 of leucogaster alone. 



The colors* are highly characteristic. The snowy-white of the whole 

 under parts and feet of leucogaster is replaced by a yellowish-white, or an 

 extremely pale buff or fawn. The dark stripe along the top of the tail is 

 very narrow, and falls considerably short of the tip, which is wholly whitish. 

 The whole muzzle is whitish, as in leucogaster ; the fluffy hairs about the ears 

 give rise to a pale patch in front of each, which, with the dusky body of the 

 ear and its silvery edging, produce a parti-coloration not seen in leucogaster. 

 The entire upper parts are of a warm though rather light brownish-fulvous, 

 entirely different from the gray mouse-brown which leucogaster usually 

 exhibits, and, moreover, without appreciable darker dorsal area. The line 

 of demarkation along the sides is abrupt, as in leucogaster. 



The animal is apparently somewhat smaller than an average leucogaster, 

 but not much so, and not less than some specimens of the latter. No. 9886 

 measures, nose to eye, 0.50 ; to ear, 0.95; to occiput, 1.25; to root of tail 



"Our type has been skinned out of alcohol; still, we are not snro that tho fluid has appreciably 

 affected tho coloration, for specimens of leucogaster which have lain iu spirits a much longer time are not. 

 changed perceptibly. ^ 



