The Chipmunks of the Genus Eutamias. 201 



two forms in question speciosus and callipeplus are separated, 

 if at all, by a gap only 15 miles in width. 



In view of these facts it is important to bear in mind that the 

 southern part of the lofty Sierra is split lengthwise by the upper 

 valley of Kern River into two parallel ridges, one of which (the 

 eastern) is inhabited by true speciosus, the other (the western) 

 by callipeplus. It should be remembered also that the Mt. Pinos 

 colony of callipeplus lies southwest of the Sierra colony, and that 

 the San Bernardino Mt. colony of speciosus lies southeast of the 

 Sierra colony of the same form. These facts, taken in connec 

 tion with the close relationship of speciosus with quadrivittatus of 

 Colorado, point to the former continuous range of the group 

 across the south end of the Great Basin from the Rocky Mts. to 

 the Sierra, San Bernardino Mt., and San Jacinto Peak ; while the 

 presence of a distinct form (callipeplus) on Mt. Pinos at the ex 

 treme west end of the Mohave Desert and on the western range 

 of the Sierra not only points to a former connection between the 

 now separated colonies of this form* by way of Tehachapi and 

 the intervening low mountains, but also seems to show that the 

 two existing colonies of true speciosus now separated by the Mo- 

 have Desert were never united unless in very remote times 

 by continuity of range along the horseshoe of mountains which 

 connect the San Bernardino range with the Sierra. These facts 

 argue great antiquity for the speciosus-quadrivittatus type and 

 seem to show that very little change has taken place during the 

 many thousands of years that have elapsed since the climate 

 was cool enough to admit of continuity of Boreal forest across 

 what are now the torrid Sonoran deserts of eastern California, 

 southern Nevada, and southwestern Utah. This view receives 

 additional support from the large amount of differentiation 

 undergone by the colonies of clearly derivative forms of these 

 animals now stranded on isolated mountains within the area 

 of former continuous range of quadrivittatus-speciosus across the 

 southern part of the Great Basin. These forms are the subspe 

 cies inyoensis of the Inyo and White Mts., and the very distinct 

 species palmeri of the Charleston Mts., both of which must have 

 developed their distinctive peculiarities since the great change 

 in climate took place. And it is interesting to note that the 

 degree of differentiation of these forms is proportionate to the 

 climatic isolation of their homes. 



