SCIURIDAX—GEOGRAPHICAL DISTRIBUTION AND VARIATION. 649 
size. Beginning at the northward, we find that specimens from as far south 
as Pembina, and thence northward, are quite undistinguishable from speci- 
mens from Northeastern Asia, or the so-called Tamias ‘pallasi’ (T. pallasi 
Baird = T. striatus of most European authors). This form is found to only 
a limited extent south of the northern boundary of the United States, where, 
on the plains of the Upper Missouri, it passes into the blanched, pallid form 
of T. quadrivittatus (T. quadrivittatus var. pallidus nobis,—see beyond), and 
further westward into the true T. quadrivittatus of the Rocky Mountains, and 
still further westward into the so-called 7. townsendi of the Pacific coast. 
In this group, the greatest pallor is reached on the plains of the Yellowstone, 
and in the deserts of Nevada, Utah, and Arizona. In the central portions of 
the Rocky Mountains (Colorado and portions of New Mexico), a form is devel- 
oped, distinguished by its generally bright, strong colors, but especially for 
the rich fulvous tints of the sides of the body, to which there is but a slight 
tendency either in the northern form or the pallid form of the plains. Both, 
however, very gradually pass into the rufous-sided type, the pallid form 
wherever the plains approach the mountains (as along the eastern base of 
the Rocky Mountains, the Uintah, Sierra Nevada, and others of the more 
southern ranges), gradually becoming fulvous, while the darker northern form 
grades into the larger fulvous race of the more northern portions of the Rocky 
Mountains in Montana and Idaho. This larger fulvous race west of the main 
divide soon begins. to assume a duller, more fuscous shade, deepening finally 
into the very fuscous form (7. fownsendi) of the region between the Cascade 
Range and the Pacific coast. In this furm, the general color increases so 
much in depth as to become dusky yellowish-brown, and both the light and 
the dark stripes become obscure, and occasionally almost entirely obsolete, 
through the gradual accession of color. Between the extreme phase of this 
fuscous type and the extreme phase of the pallid type of the Plains, in which 
the stripes are sometimes again partially obsolete, through the extreme light- 
ness of the general color, the differences are very great indeed. Yet in 
placing the scores of specimens I have had the opportunity of examining in 
a geographical series, or arranging them simply according to their localities, 
a most thorough and minute intergradation becomes at once apparent. ‘The 
difference in size, too, between northern and southern specimens, is also 
unusually great; the pale, southern form of the Plains, and the extremely 
bright, fulvous form of Colorado and New Mexico, being very much smaller 
