Allen,] 282 [Februarys 



fuscous shade, deepening finally into the very fuscous form (T. Town- 

 sendi) of the region between the Cascade Range and the Pacific 

 Coast. In this form the general color increases so much ki 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 lightness 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 arrang- 

 ing 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 

 than the northern, darker form, or than the fuscous type of the north- 

 west 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 

 Tamias quadrivitatus occur the dark types of Sciurus hudsonius, and 

 the dark-backed form of Spermophilus grammurus, and also a peculiar, 

 dusky form of Arctomys and of Lepus, and a dark form of Spermophi- 

 lus Richardsoni. On the plains occur pallid forms of Sciurus "ludo- 

 vicianus" Sciurus hudsonius, Tamias quadrivitatus, and Spermophilus 

 Richardsoni. With the fulvous type of Tamias quadrivitatus occurs a 

 rufous form of Spermophilus grammurus] but the form of Scuirus 

 hudsonius, occurring over the same area, presents the exceptional 

 condition' of a minimum amount of rufous. 



Taking the mammals and the birds of the continent collectively, 

 we may recognize, in a general way, at least five more or less well- 

 marked areas characterized by certain peculiarities of color variation, 

 and also a correlation between these areas and the prevalent tenden- 

 cies of color increase and the amount of aqueous precipitation. Other 

 lesser areas, characterized by certain peculiarities of color variation, 

 will doubtless be recognized when the material at hand is sufficient to 

 admit of a more detailed examination of the subject, such indications, 

 in fact, being already more or less apparent. The first region we 



