1874. 281 [Allen. 



above, and in having the ventral surface more or less strongly tinged 

 with buff, varying in different specimens from cinerous to pure buff. 

 This form prevails from the Cascade Range to the Pacific Coast, 

 southward to Northern California, and northward probably to Sitka. 

 In Northern California the S. Douglassi meets the range of the true 

 S. Fremonti, between which two forms there is here the most gradual 

 and intimate intergradation. In this group we have hence four form3 

 which, in their extreme phases of mutual divergence, appear as di- 

 verse as four good, congeneric species need to, but which, at points 

 where their respective habitats join, pass into each other as gradually 

 as do the physical conditions of the localities at which their extreme 

 phases are developed. 



The Tamias quadrivitatus group 1 presents an equally or even more 

 striking range of variation in color, and also varies to an unusual de- 

 gree in size. Beginning at the northward, we find that specimens 

 from as far south as Pembina, and thence northward, are quite undis- 

 tinguishable from specimens from Northeastern Asia, or the so-called 

 Tamias " Pallasi " (T. PaUasi 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. quadri- 

 vitatus (I 7 . quadrivitatus , var. pallidus nobis, — see beyond), and further 

 westward into the true T. quadrivitatus of the Rocky Mountains, and 

 still further westward into the so-called T. 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 developed 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 north- 

 ern form or the pallid form of the plains. Both, however, very grad- 

 ually 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 south- 

 ern 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 



1 Tamias quadrivitatus, T. Pallasi, T. Townsendi and T. dorsalis of American 

 authors. 



