650 MONOGRAPHS OF NORTH AMERICAN RODENTIA, 
than the northern, darker form, or than the fuscous type of the northwest 
coast, 
‘“‘ As corroborative evidence that these varied types of coloration are but 
geographical races, it becomes interesting to observe that the light and dark 
and the fulvous and rufous forms, respectively, of the different species, occur 
over the same areas. With the fuscous type of Tumias quadrivittatus occur 
the dark types of Scirus hudsonius, and the dark-backed form of Spermo- 
philus grammurus, and also a peculiar dusky form of Arctomys and of Lepus, 
and a dark form of Spermophilus richardsoni. On the Plains occur pallid 
forms of Sctiurus ‘ludovicianus’, Sciurus hudsonius, Tamias quadrivitiatus, and 
Spermophilus richardsoni. With the fulvous type of Tamias quadrivittatus 
occurs a rufous form of Spermophilus grammurus; but the form of Sciurus 
hudsonius, occurring over the same area, presents the exceptional condition 
of a minimum amount of rufous.” 
“In addition to the tendency to change of color with locality, there is 
another phase of color variation that requires, in this connection, a passing 
notice,—namely, melanism. It is now well known that almost every species 
of Mammal may be expected to present melanistic individuals, instances of 
its occurrence in the majority of the North American species being now well 
established. Indeed, the very fact of a melanistic phase of coloration may 
be looked upon as almost @ priori evidence that the individuals presenting it 
belong toa melanistic race of some species whose normal color is some other 
tint than black, as Professor Baird long since remarked in respect to the 
American Squirrels. It has been supposed that the tendency to melanism is 
more prevalent at the northward; but such does not appear to be necessarily 
the case. Among the Sciurida, for instance, a group rather remarkable for 
a tendency to melanistic varieties, the black and dusky forms are as often 
southern as northern. In some species, melanistic individuals are as rare as 
are the cases of albinism, as in Sciurus hudsonius, the species of Tamias, and 
in many of the Spermophili, while in others they are sometimes the common, 
if not the prevalent, form over a considerable area, as occurs in «Sciurus caro- 
finensis and Sccurus cinereus. Melanism is also of frequent occurrence in 
Scrurus aberti [*] and in Spermophilus grammurus; the latter presents a melan- 
istic form both in Texas and Lower California. Spermophilus parryi has also 
a black race along the Yukon River, and frequent instances of melanism are 
[* Melanism of this species largely predominates over the normal coloration in Colorado.] 
