Fourth upper tooth smaller than first and about equal to second and 

 third; bulla present but depressed; short auditory meatus present 

 Scapanns Western Mole 



57. Two tiny incisors behind the upper two large ones 58. 

 Only two upper incisors 60. 



58. Skull not particularly high, not spongy before orbits; five upper cheek 



teeth on each side; no post'orbital processes 

 Ochotona Pika 

 Skull high, spongy before orbits; six upper cheek teeth on each side, last 

 one very small; post-orbital processes present 59. 



59. A more or less diamond-shaped bone (inter-parietal) between parietals 



and supra -occipital; post-orbital processes diverging from cranium 



Lepus Jack Rabbit and Domestic Rabbit 

 No inter-parietal evident in adult; post-orbital processes lying close to 

 cranium, leaving only a slight notch 



Sylvilagus Cottontail Rabbit 



60. With distinct post-orbital processes; very small ante-orbital opening 



(Squirrel Family) 61. 



No definite post-orbital processes; ante-orbital opening large or small 72. 



61. About three and one -half inches long; skull flattened on top, concave be- 



tween orbits; post-orbital process with posterior edge at right angles to 

 median line of skull; incisors about as wide as deep 

 Marmota Woodchuck 

 Smaller; skull convex; post-orbitals directed posteriorly; incisors narrow 

 and deep 62. 



62. Ante-orbital opening a vertical slit 63. 

 Ante-orbital opening oval or triangular 65. 



63. Skull about one and three-quarters inches long; nasals one-fourth the 



length of the skull 



Tamiasciurus hudsonicus Red Squirrel 

 Skull about two and one-half inches long; nasals one-third the length of 

 the skull 64. 



64. Five cheek teeth above on each side, the first small and sometimes lost 



Sciurus carolinensis (and relatives) Eastern Gray Squirrel 

 Four upper cheek teeth 



Sdurus niger (and relatives) Fox Squirrel 



65. Zygomatic bar, as seen from above, following the curve of the skull 66. 

 Zygomatic bar, as seen from above, projecting decidedly from side of 



cranium 68. 



66. A definite notch in middle of upper rim of orbit 



Glaucomys Flying Squirrel 

 Notch, if present, not in middle of upper rim of orbit 67. 



67. Four upper check teeth on each side, the rows converging posteriorly 



Tamias Eastern Chipmunk 

 Five upper cheek teeth, the rows parallel 

 Eutamias Western Chipmunk 



530 



