86 



MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



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

 each other. They never gain either the rich "brown" of Massachusetts leu- 

 copus 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, then, 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 whether we retain the name 

 or not. But, of course, after 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 "var.", can we look upon 

 it as expressing a pure geographical race; for unquestionable leucopus occurs 

 throughout the United States range of "sonoriensis", and everywhere the 

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

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

 palest, or grayest specimens. 



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 our discussion 

 of Hesperomys "eremicus". 



Tabu: XXI. — Measurements of twelve specimens of Hesperojiys like leucopus from Fort Cobb. 



Locality. 



Collivtor. 



■3 J 



a 



n 



Remarks. 



Fort Cobb . 



do .... 



do .... 



do .... 



do .... 



do .... 



do .... 



do .... 



do.... 



do .... 



do .... 



do .... 



E. Palmer 



do... 



do ... 



do... 



do ... 



do ... 



4.00 

 3.20 

 2.75 

 3.00 



3.00 

 3.00 

 2.30 

 2.70 



0.36 

 0.35 



0.85 

 0.85 



0.79 

 0.80 



0.56 

 0. 62 



0.58 



.do . 



...do. 

 ...do. 

 ...do. 

 ...do . 

 ...do. 



3.40 

 3.00 

 3.00 

 2.60 

 3.50 

 3.40 

 3.10 



2.30 

 2.40 

 2.30 

 2.50 

 2. 50 

 2.90 

 2.90 



0.31 

 0.33 

 0.33 

 0.36 

 0.33 



0.82 

 0.80 

 0.80 

 0.82 

 0.79 

 0.79 

 0.82 



0.60 

 0.50 

 0.57 

 0. 55 



0.60 



Dry; stretched. 



Dry. 



Dry ; shrunken. 



Dry. 



Yonng. 



Dry; stretehed. 



Dry. 



...do. 



...do. 



Dry ; stretched. 



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 absolutely identical with an average Massachusetts skin. In 



