MURIDAL—SIGMODONTES—HESPEROMYS LEUCOPUS. 65 
It seems unnecessary for us to examine the figures of this table in detail 
after what we have said of the Massachusetts lot. Bringing together so many 
specimens, we find, does not appreciably affect the Jenks’ average ; but it has 
the inevitable result of spreading the extremes a little farther apari, and 
proving the range of variation to be rather more than we allowed in the former 
case—in fact, it demonstrates the variability of the species to be fully as great 
as claimed by Alien. 
Contrary to our expectation, we do not find im this series any evidence 
that datitude exerts an appreciable influence upon the absolute size or relative 
proportion of the parts of this mouse. Nor do we observe any difference 
with latitude in the character of the pelage, the hairiness of the soles or tail, 
&c.—at any rate to an appreciable extent—and certainly no such difference 
as may be observed between summer and winter specimens from the same 
locality (when we come, however, to bring in Arctic skins, as below, we 
shall be able to see a difference). In the matter of color, there is positively 
nothing in this whole series that we cannot exactly match among Massachu- 
setts skins. And yet if is curious to observe that almost every considerable 
geographical area within the limits represented in the table produces a slight 
strain or breed of its white-footed mice—some difference in color indescriba- 
ble in words, but which strikes the eye that is very familiar with the subject. 
The Nova Scotian animal and the Virginian, the Illinois and the Kansas, are 
always distinguishable. We venture to assert that we can distinguish in 
North America about éwenty kinds of Hesperomys leucopus wpon characters at 
least as constant, reliable, and tangible as those hitherto held to define the 
greater part of the “species” that have been in vogue of late years. 
The first nominal species that we shall investigate is the H. “‘myoides” 
of Baird, who described his animal chiefly from Vermont specimens, identify- 
ing it with the ‘“Cricetus myoides” of Gapper. The only characters ascribed 
to it are: first, possession of cheek-pouches; secondly, ‘‘tail-vertebrae gen- 
erally 0.25 of an inch longer than head and body.” But we have just shown 
that the possession of a tail a fourth (or more) of an inch longer than the 
body has no significance whatever as a specific character ; and among the 
specimens enumerated by Baird (and also tabulated by us) are some with the 
tail no longer than the body, and others with the tail shorter than the body ; 
oM 
