84 NEW YORK STATE MUSEUM 



The order G li r e s is essentially cosmopolitan. Its members may be 

 recognized at a glance by their peculiar teeth. The group is usually 

 divided into 21 families,^ nine of which occur in North America. Six of 

 these are found within our limits. 



FAMII.IES OF GI.IRES 



Upper front teeth four, the second pair raiuute and 

 placed directly behind the tirst (bares, Du- 



plicidentata) Leporidae, p. 115 



Upper front teeth two. (Simplicidentata) 

 Tail very broad, flattened from above downward 



(beaver) Castoridae, p. 91 



Tail rounded or flattened from side to side 

 Fur thickly sprinkled with stiff" quills (por- 

 cupines) Erethizontidae, p. 115 



Fur without quills 

 At least four well developed grinding teeth in 



each jaw; tail bushy (squirrels, etc.) Sciuridae, p. 84 



Never more than three well developed grind- 

 ing teeth in each jaw ; tail closely haired 

 Hind feet not greatly elongated (rats, mice 



etc.) Muridae, p. 92 



Hind feet greatly elongated { jumping mice) Dipodidae, p. Ill 



Family Sciuridae Squirrels 



Upper front teeth two ; upper cheek teeth four or five, lower cheek teeth four ; 

 a well developed bony projection on skull above and behind eye socket (postor- 

 bital process) ; tall round, covered with long hairs which are usually so arranged 

 as to form a broad, flat brush. (Sciuridae ; genus S c i u r u s) 



The family Sciuridae is almost cosmopolitan in distribution. It is 

 a large group, containing 15 or 20 genera. In North America it is repre- 

 sented by seven genera, four of which occur within our limits. 



GENERA OF SCIURIDAE 



Sides with a densely furred membrane joining front 



and hind legs (flying squirrels) Sciuropterus, p. 90 



Sides without membrane 

 Form stout and clumsy ; tail less than half as long 



as body ; top of skull nearly flat (woodchucks) Arctomys, p. 89 

 Form slender and graceful; tail much more than 

 half as long as body; top of skull distinctly 

 rounded 

 Cheek pouches present; back striped (chip- 

 munks) Tamias,p. 88 



Cheek pouches absent; back (in our species) 



without stripes (squirrels) Sciurus, p. 85 



1 Tullberg recognizes 27 families, but even this number Is probably too small. 



