114. East of the Rockies 



Zapus hudsonius (Zimmermann) Hudson Bay Jumping Mouse 

 In the Rocky Mountain region and westward 115. 



115. Under parts much the same color as the upper parts; coastal regions of 



Cal. 



Zapus oranus Prehle Coastal Jumping Mouse 

 Under parts white or only slightly tinged with the color of the upper 

 parts 116. 



116. Tail indistinctly bicolor; Rocky mountain region 



Zapus princeps Allen Rocky Mountain Jumping Mouse 

 Tail sharply bicolor — gray above, white below 117. 



117. With a distinct, dark dorsal band; Pacific states 



Zapus trinotatus Rhoads Oregon Jumping Mouse 



(Often considered to be a subspecies of the preceding.) 

 No distinct, dark dorsal band; Oregon and Cal. 



Zapus pacificus Merriam Pacific Jumping Mouse 



118. Grinding teeth of the upper jaw with rounded points in two or three 



lengthwise rows on the crowns 119. 



Grinding teeth with flattened crowns showing loops or irregular, tri' 



angular folds of enamel; Family Cncetidae (part) Native Rats and 



Mice 144. 



119. With the rounded points on the grinding teeth extending in three length- 



wise rows; tail practically hairless; introduced species; Family Muridae 

 Old World Rats and Mice 120. 



With the rounded points on the grinding teeth extending in two length- 

 wise rows; tail usually hairy; native species; Family Cncetidae (part) 

 Native Rats and Mice 123. 



120. Total length of adult six to seven inches 



Mus musculus Linn. House Mouse 

 Total length fifteen to seventeen inches 121. 



121. Length from nose to root of tail greater than, or occasionally equal to, 



length of tail; grayish or brownish above, gradually shading to lighter 

 below 



Kattus norvegicus (Erxleben) Norway Rat, Common or House 

 Rat 



(Mus norvegicus or Epimys norvegicus of some writers) 

 Length from nose to root of tail less than length of tail; blackish above 

 or else yellowish- white below 122. 



122. Slate colored to black above; slaty-gray to black below 



Rattus rattus rattus (Linn.) Black Rat 

 Reddish-brown above; yellowish-white below 



Rattus rattus alexandrinus (Geoffrey) Roof Rat 



123. Upper incisors with deep lengthwise grooves 124. 

 Upper incisors not grooved on front 128. 



124. Grayish below; Virginia to Florida and Louisiana 



Reithrodontomys humuhs (Audubon and Bachman) Harvest 

 Mouse 

 White to buff below; west of the Mississippi River 125. 



516 



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