1911] Taijlor: Mammds of the 1909 Nevada Expedition. 271 



postero-external angle of the maxillary arch in the Nevada speci- 

 mens is not nearly so prononnced, or produced so much back- 

 ward, as in columhianus, being nearer levipes in this respect. A 

 tendency seems to exist in the Nevada animals to have the nasals 

 more spread anteriorly than in either species. 



The angle of the mandible varies greatly in all the specimens. 

 Our series seem to have sharper angles than either of the others. 

 One example of levipes (no. 40641) has the angle sharp, as in 

 the Nevada series; the other (no. 41340) has it much more blunt. 

 There is in this respect also more difference between these two 

 specimens than between the Quinn River series and the average 

 of either levipes or cohnnhianus. 



Not one of the skulls resembles those of topotypes of colmn- 

 hianus. While not typical of the form, they are certainly nearer 

 levipes. However, the lot is nearly as well marked off from 

 levipes as is eolumhianus; this is not nearly as startling a state- 

 ment as it might seem, for a consideration of available topotypes 

 of the two shows them to be closely related. The Quinn River 

 animals are certainly a fairly well-marked local race. 



Distribution. — Ten specimens of Perodipus microps levipes 

 were definitely recorded : from Quinn River Crossing (4100 feet), 

 8; from Big Creek Ranch (4350 feet), 1; from Virgin Valley 

 (5000 feet), 1. These records serve to extend the known range 

 of levipes with its variants to the northern part of the Great 

 Basin. Bailey (1908, p. 22) mentions this as one of the species 

 found in the Carson Sink and some of the neighboring valleys. 

 Zonall}' its distribution is purely Upper Sonoran. 



Fig. 2. Side and top views (diagrammatic) of burrow of kangaroo rat. 



