IH 



^]: 



86 



MONOGRAl'HS OP NORTH AMERICAN RODENTIA. 



[ 



respect, Ihcy differ more from both leucopus and sonoriensis than these do from 

 each other. Tlicy never gain either the rich "brown" of Massachusetts ku- 

 C'pus nor the silvery-gray or light fulvous of sonoriensis. They are nearer 

 the house-mouse in color; the dark dorsal gray-brown washing over all the 

 upper parts and the white below being far from snowy. 



It is evident, tiien, that the coloration of these short-tailed mice of Inte- 

 rior and Arctic America cannot form part of a specific diagnosis. 



Thus we have endeavored to show exactly what "sonoriensis" amounts 

 to; and this done, it is a matter of indifference wliether we retain the name 

 or not. But, of course, afler this exhibit, the animals bearing it cannot be 

 considered specifically distinct from leucopus. Nor, in retaining the name, as 

 we have judged it best to do, qualified by the sign "van", can we look upon 

 it as expressing a pure geograpliical race; for unquestionable kucopus occurs 

 throirghout the United States range of "sonoriensis'', and everywhere the 

 intergradation is perfect. In labeling our immense series, we sliall hesitate 

 to write "variety sonoriensis" on the placard of any but the shortest-tailed, 

 palest, or grayest specimens. . , i , j .^ , 



Before leaving the subject, we will examine an interesting series of skins 

 from Fort Cobb, which will point our above remarks, and then notice some 

 very instructive sets from Arizona, which pave the way for onr discussion 

 of Hesperomys "eremicus". 



Tabu: WL—McmnremenU of tweke specimens of Hbbfeiiomvs like leucopus fivm Fort Cobb. 



Locality. 



Fort Cobb . 



ilo .... 



do .... 



do.... 



do.... 



do.... 



.. ..do .... 



do .... 



do.... 



do.... 



do.... 



do.... 



Collector. 



£. Palmer . 



do... 



do..., 



do... 



do..., 



do... 



.do . 



do... 



do... 



do... 



do... 



do... 



H 



4.00 

 J. SO 



a 75 

 aoo 



3.40 

 3.00 

 3.00 

 9.60 



a.'iO 



3.40 

 3.10 



3.00 

 3.00 

 S.30 

 170 



3.30 

 3.40 

 3.30 

 3.50 

 S.iiO 

 3.90 

 3.90 



0.36 

 0.33 



0.31 

 0.33 

 0.31 

 0.31! 

 0.33 



M 



o.es 



0.85 

 0.79 

 0.80 



0.83 

 0.80 



o.eo 



0.83 

 0.70 

 0.10 

 0.83 



o.sa 



0.63 



ft58 



0.60 

 0.50 

 0.57 

 0.55 

 0.60 



Beuiarka. 



Dry ; atrotched. 



Dry. 



Dry; ahmnken. 



Dry. 



Yoang. 



Dry I Etretnbwl. 



Dry. 



..do. 



...do. 



Dry I alntohed. 



Dry. 



This series is, perhaps, referable to sonoriensis on grounds of locality, 

 but it is positively indistinguishable from ordinary leucopus. No. 9251, for 

 example, is ab,solutely identical with an average Massachusetts skin. In 



':|l' 



