XII 
Illustrations 
FIG. PAGE 
45. House Mouse, Mus musculus, skull, showing 
dentition . . . . . . .139 
46. Beaver, Castor canadensis frondator, skull, show- 
ing dentition . . . . . -141 
47. Beaver, Castor canadensis frondator, side view 
of skull ....... 142 
48a. A Beaver Dam .... facing p. 142 
48b. Tree cut by Beaver . . . '< j^^2 
48c. A Beaver House . . . . " 143 
48d. Beaver House cut open . , " "143 
48. Beaver, Castor canadensis frondator . . 143 
49. Western Woodchuck, Marmota flaviv enter , skull, 
showing dentition . . . . .146 
50. Western Woodchuck, Marmota flaviventer . 147 
51. Plains Prairie Dog, Cynomys ludovicianus, sknll, 
showing dentition . . . . .149 
52. White-tailed Prairie Dog, Cynomys leucurus . 154 
53. Large Spotted Spermophiles, Citellus spilosoma 
major . . . . . . .158 
55. Say's Ground Squirrel, Callospermophilus late- 
ralis ........ 167 
56. Say's Ground Squirrel, Callospermophilus late- 
ralis, and Related Chipmunk, Eutamias 
minimus consobrinus . . . . .169 
57. Skins of Chipmunks . . . . . 172 
58. Related Chipmunk 180 
59. Plain-backed Squirrel, Sciurus aberti ferreus, 
skull, showing dentition . . . .182 
