12 



NORTH AMERICAN FAUNA 66 



4a. Coloration of sides orange; tail often tipped with white 



Napaeozapus insignis (woodland jumping mouse) 

 b. Coloration of sides yellowish; tail never tipped with white 



Zapus hudsonius (meadow jumping mouse) 



5a. Tail bushy 6 



b. Tail not bushy 10 



6a. Fore and hind limbs connected by a loose fold of skin; adapting the ani- 

 mal for gliding Glaucomys volans (southern flying squirrel) 



b. Fore and hind limbs not connected by a loose fold of skin 7 



7a. Tail less than one-quarter of the total length. _ Marmota monax (woodchuck) 



6. Tail greater than one-third of the total length 8 



8a. Coloration reddish-brown above; under 325 mm. in total length 



Tamiasciurus hudsonicus (red squirrel) 



6. Coloration not reddish-brown; over 325 mm. in total length 9 



9a. Coloration of upper parts gray, darker along middle of back; under 

 550 mm. in total length; upper premolars 2-2 



Sciurus carolinensis (gray squirrel) 

 b. Coloration of upper parts variable-grayish, reddish, or bufify, but sides 

 not noticeably paler than back; over 550 mm. in total length; upper 



premolars 1-1 Sciurus niger (fox squirrel) 



10a. Coloration on back reddish, marked with several longitudinal black and 



white stripes Tamias striatus (eastern chipmunk) 



6. Back not striped 11 



11a. Tail flattened horizontally, paddle-like Castor canadensis (beaver) 



b. Tail not horizontally flattened 12 



12a. Tail compressed laterally Ondatra zibeihicus (muskrat) 



b. Tail not compressed laterally 13 



13a. Total length over 325 mm 14 



b. Total length less than 275 mm 17 



14a. Total length over 500 mm.; aquatic in habits. _ Myocastor coypus (nutria) 



6. Total length less than 500 mm 15 



15a. Tail length equal to, or more than, half total length of animal 



Rattus rattus (black rat) 



b. Tail length less than half total length 16 



16a. Tail well haired, and not conspicuously scaly 



Neotoma floridana (eastern woodrat) 

 b. Tail scantily haired and noticeably scaly. Rattus norvegicus (Norway rat) 

 17a. Tail very short, equal to about one-sixth of total length 



Pitymys pinetorum (pine vole) 



b. Tail longer than one-sixth of total length 18 



18a. Tail only moderately short, equal to about one-third of the total length. _ 19 



b. Tail longer than one-third of total length 20 



19a. Back marked with a wide band of dull red from forehead to rump 



Clethrionomys gapperi (red-backed vole) 

 b. Back dark brown to nearly black.. Microtus pennsylvanicus (meadow vole) 

 20a. Line of demarcation between coloration of back and abdomen indistinct; 



coloration often uniform gray throughout.. Mus musculus (house mouse) 

 6. Sharp line of demarcation between coloration of back and abdomen; 



abdomen always white 21 



21a. Total length over 225 mm Oryzamys palustris (rice rat) 



b. Total length under 200 mm 22 



