xv PRAIRIE DOGS 465 



Arctomys ; the molars are five in the upper and four in the lower 

 jaw. The caecum is relatively speaking very small ; the measure- 

 ments in a specimen of S. tredecimlineatus, dissected by Dr. 

 Tullberg, were: small intestine, 580 mm.; large intestine, 170 

 mm. ; and caecum, 27 mm. In Tamias also the caecum is not 

 greatly developed. These animals are burrowing in habit. 



The Prairie-dogs, genus Cynomys, of which the best-known 

 species is perhaps C. ludovicianus, are very like the Squirrels, but 

 they are not arboreal creatures ; they live in burrows on the 

 ground, as their vernacular name denotes. The genus is entirely 

 North American, and four species have been differentiated. 



The Prairie-dos or Prairie-marmot is some 10 inches to one 



FIG. 233. Long-tailed Marmot. Arctomys caudatus. x f . 



foot in length. The tail is no more than 2 inches. The ears 

 are very small ; the thumb is fully developed and bears a claw. 

 The measurements of the various sections of the intestine are the 

 following: Small intestine, 860 mm.; large intestine, 690 mm.; 

 caecum, 75 mm. Thus the caecum is not large comparatively 

 speaking. These animals dig burrows on grassy plains which 

 they share with the Ground Owl (Speotyto cunicularis} and with 

 Eattlesnakes, all three species appearing to live in perfect amity. 

 Probably the Owls use the conveniently-constructed burrows, and 

 the Eattlesnakes come there to look after the young of both. 



Closely allied to the last are the Marmots, genus Arctomys. 



They differ in the rudimentary character of the thumb and in the 



longer tail. The' eyes and ears are small. The distribution of 



the genus is Nearctic and Palaearctic. There are ten species of 



VOL. x 2 H 



