Family CRICETIDAE 



159 



(125-150 mm.); hind foot %—}i inch (15-18 mm.); ear from 

 notch about Yi inch (11-14 mm.). 



The skull is 22.0-24.5 mm. (about ?n-l inch) long; its width 

 across the zygomatic arches just behind the intraorbital plate is 

 less than 12 mm. Dental formula: 1 1/1. C 0, Pm 0/0, 



M 3/3. 



The deer mouse may usually be distinguished from the more 

 abundant white-footed mouse on the basis of the following com- 

 bination of characters: hind foot less than 19 mm. long, rather 

 than 19 mm. or more as in the white-footed mouse; tail less 

 than 60 mm. long, rather than more than 60 mm.; total length 



Fig. 89. — Deer mouse. 



of adults less than 155 mm., rather than more; width of skull 

 across zygomatic arches just behind the infraorbital plate less 

 than 12 mm., rather than more; length of skull 14.5 mm. or less, 

 rather than more. 



Life History. — The deer mouse is an inhabitant of the 

 prairie and is most abundant in areas of ungra/.ed and uncut 

 grass and forbs, such as grow along railroad and highway rights- 

 of-way, in extensive weedy fields, and along fencerows, fig. 2. 

 It is at home under a haystack or a corn shock, among dry 

 weeds along a fence, or under a rock or board. 



The nest, usually underground, is approximately the size of a 

 man's two cupped hands. It is formed of a coarse outer frame- 



