480 



U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



leucopus ; they are thin, membranous, and sparsely clothed with scant hairs. The tail is very 

 long, considerably exceeding the body ; it is more finely annulated than in H. leucopus, and 

 covered with hairs, which, however, do not conceal the annuli. 



The hair of this species is quite long, though not particularly soft. The upper parts are of a 

 light grayish yellow, finely lined by the black tips of the hairs ; the cheeks and lower part of 

 sides with rather a distinct stripe of light ochrey yellow. The under parts and the feet are 

 pure white ; the tail is uniform in color, or, at most, a little lighter beneath, the line of sepa 

 ration entirely inappreciable. 



The colors of this species are more yellow, and much lighter, in every way, than in H. 

 leucopus. It is much smaller and lighter colored than H. cali/ornicus, in which we have 

 similar characters of naked soles, very long and unicolor tail, &c. 



List of specimens. 



HESPEROMYS (ONYCHOMYS) LEUCOGASTER. 



Missouri Mouse. 



Hypudaeus leucogatter, PRINZ MAX. Reise in das innere Nord-Amerika, II, 1841, 99. (Fort Clark.) 

 Mm Missouriensii, AUD. & BACH. N. Am. Quad, II, 1851, 327 ; pi. c. 



SP. CH. Color above, grayish brown, passing into yellowish red, and finally into a stripe of fulvous on the sides. Feet, 

 including outer surface of the fore arm and under surface of the body and tail, white. For generic characters see page 458. 



This species, in some respects, bears a resemblance to Arvicola, especially in the short tail, 

 and rather short ears ; it is in general appearance, however, nearer to the ordinary white-footed 

 mice. Still, in many respects, there is a striking difference from both, to be hereafter 

 referred to. 



The head is proportioned much as in Hesperomys leucopus, though with a broader muzzle ; th<! , 

 muzzle is entirely hairy, except on the septum ; there is rather more hair than in H. Uucopus. 

 The lip is cleft nearly to the septum. The eyes are large, the whiskers long, and white and 

 black. The ears are small, about two-thirds the height, and half the area of H. leucopus. Th 3 

 antitragus is low and very slightly valvular, less so than in H. leucopus. The membrane is 

 rather thick, the surfaces of the ear well coated with short hairs, longest on the convexity, an 1 

 nearly naked around and anterior to the meatus. 



The most conspicuous feature of this mouse is in the peculiar proportions of the limbs. The 



