34 PROCEEDINGS OF THE ACADEMY OF [1895. 



brown vent and fulvous suffusion of throat and breast characteristic 

 of more northern specimens. A comparison of the skulls of these 

 soon showed constant and specific peculiarities, the most striking being 

 the posterior rounding of the frontal bones of San Diego County speci- 

 mens contrasted with the peculiar right-angled aspect of the fronto- 

 parietal sutures in typical Peromyscus californicus. 



The ears of the southern species are much larger even than those 

 of californicus and the size of the animal in length measurements 

 considerably exceeds its rival. 



The two have been confounded in previous descriptions and the 

 southern form is probably responsible for the apparently exaggerated 

 statements of the dimensions of typical californicus. 



I am at a loss to account for the conditions described by Dr. J. 

 A. Allen 3 regarding certain specimens of Peromyscus of the califor- 

 nicus type from Santa Ysabel and Dulzura being darker and smaller 

 than those from Santa Clara County, my own series showing exactly 

 reversed characters. 



I may also state in this connection that none of my specimens 

 from either locality have white-tipped tails. 



3. Thomomys altivallis sp. nov. Type, ad. £ , No. 1,927, Col. of S. N. Rhoads, 

 San Bernardino Mts., California (alt. 5,000 ft.). Col. by E. B. Herron, 

 Aug. 10, 1894. 



Description. — Size medium, smaller than T. toltecus Allen, but 

 larger than T. monticolus Allen. Above dull chestnut-brown, be- 

 coming darker dorsally and along upper sides of head, the middle 

 crown and median line of back nearly black, the sides washed with 

 fulvous. Nose, chops, and ears, dusky, the latter being bordered 

 anteriorly by a narrow line, and beneath and behind by a broad 

 patch of sooty black reaching nearly to occiput. Beneath plum- 

 beous-gray, washed with rusty (the plumbeous in worn specimens 

 strongly predominating). Throat, feet, and legs normally of the 

 same color as rest of under parts ; tail grayish. In the type there 

 are albinistic white patches across throat, on forelegs, and at root of 

 tail. 



Skull long and narrow, the zygomae tapering toward the rostrum, 

 which is relatively long and wide. Interparietal narrow and (in the 

 type) longer than wide; nasals rather long and acutely pointed on 



3 Bull. Amer. Mus. N. Hist., 1893, 187. 



