From the Eastern United States. 63 



geographically about two hundred miles. Nevertheless, the 

 conditions under which the animals live are essentially different, 

 S. canadensis confining itself to dense, preferably damp woods 

 such as Troglodytes hiemalis and Certhiafamiliaris americana choose 

 to breed in while S. americanus is a mouse of the open fields, 

 clearings, and neighborhood of houses. Only in the central and 

 southern part of its range, where the character of the country is 

 very different from that inhabited by S. canadensis, does the 

 smaller animal take to the woods with anything like regularity. 

 I have no doubt that the northward range of S. americanus has 

 been considerably extended by a gradual movement, following 

 the clearing away of the forests, thus bringing the two races into 

 their now curiously close juxtaposition. 



For the present at least I have thought it best to treat these 

 two animals as subspecies. It must be confessed, however, that 

 the number of intermediates is surprisingly small, less than a 

 dozen in the total number of specimens examined, and that these 

 occur in no particular geographical region. The case is suscep- 

 tible of no definite proof until more facts are forthcoming 

 meanwhile it lies with each. observer to treat these closely allied 

 forms as his individual preference may dictate. 



9-BiOT,. Hoc. WASH., Vot. VIII, 1893, 



