86 
MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
respect, they differ more from both deucopus and sonoriensis than these do from 
each other. 
They never gain either the rich “brown” of Massachusetts deu- 
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 deucopus. 
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 eucopus 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”. 
TABLE XXI.—Measurements of twelve specimens of HeESPEROMYS like LEUCOPUS from Fort Cobb. 
: s 3 + 
¢ Z 2/2 
3 F Date. Locality. Collector. 3 3 = 3 3 ¥ Remarks. 
a |a BH j/alea|H|a 
9251 | 9 3.00 | 0.36 | 0.85 | 0.56 | Dry; stretched. | 
9252 | 9 3.00 | 0.35 | 0.85 | 0.62 | Dry. 
9253 | J 2.30 |....-. 0.79 |..-..-| Dry; shrunken. 
9254 | 9 at ON | eee 0.80 | 0.58 | Dry. 
9 255i <2)! Mare. 9%, || 222200: cace ce cancicc soccee |sote ce QO oaacacnnecttiecslrocetell see eC al eacies | sonore || eee Young. 
9256 |.--- 2.30 | 0.31 | 0.82 | 0.60 | Dry; stretched. 
9257 | ov 2.40 | 0.33 | 0.80 | 0.50 |} Dry. 
9259 | 9 2.30 | 0.33 | 0.80 | 0. 57 a=sd0. 
9260 | ¢v 2.50 | 0.36 | 0.82 | 0.55 |....do. 
9261 | ¥ 2.50 | 0.33 | 0.79 | 0.60 | Dry; stretched. | 
9262 | ¢ PEC) ||anase 0479) eeeeee | 
9264 | o S590 0 Feeea (O82) | eee 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 
