114 Bailey The American Voles of the Genus Evotomys. 



parts of the west, they fill the whole Boreal Zone of North 

 America. In places where they range into a lower zone, local 

 conditions are such as to induce a strong mixture of boreal species 

 into the flora and fauna. This is most noticeable in the coast 

 regions. 



The material at hand shows the genus to be wonderfully uni 

 form and the species closely interrelated. No widely divergent 

 forms appear, and several of those now distinguished by names 

 can be traced by every degree of intergradation to the forms 

 from which they have become differentiated. Others in the pro 

 cess of separation have not gone far enough to warrant recogni 

 tion by name. By mapping the distribution of the several species 

 the more northern are seen to occupy much larger areas than the 

 southern. Thus the Arctic E. rutilas is common to the polar 

 parts of both continents, and the northern E. gapperi ranges from 

 the Atlantic coast to the Rocky Mountains of British Columbia, 

 while the more southern forms as carolinensis, galei, and cali- 

 fornicus are restricted to limited areas. In commenting on these 

 facts nearly ten years ago, Dr. Merriam says: " In high latitudes 

 the climatic and general physiographic conditions are compara 

 tively uniform, and boreal localities are not subject to the great 

 and sometimes sudden changes with longitude that are so fre 

 quent in temperate and tropical regions. Hence it follows that 

 the splitting up of specific types into subspecific forms from en 

 vironmental agencies is much less common within the Arctic 

 circle than farther south. IStated differently, boreal species are 

 far more stable and persistent than those inhabiting warmer 

 countries. In view of this fact, it is not surprising that the cir- 

 cumpolar E. rutilas presents but one phase throughout its entire 

 range (specimens from Scandinavia, Siberia, and Arctic America 

 being practically indistinguishable), while its more southern 

 representatives have become variously modified."* 



Generic characters. The more important generic characters of 

 Evotomys are cranial and dental, but color alone is sufficient for 

 the recognition of the North American species, and also of the 

 three European species rufocanus, glareolus, and rutilas that 

 have come into my hands. Except the gray phase in two dichro 

 matic species, all are characterized by a rufescent or reddish 

 brown dorsal stripe which extends the whole length of the back. 



*MS notes on the genus Evutomu, written in 1888, and placed at my 

 disposal by Dr. C. Hart Merriam. 



