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. ¢redecimlineatus, dissected by Dr. 
Tullberg, were: small intestine, 580 mm.; large intestine, 170 
mm.; and caecum, 27 mm. In Zamias 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-dog or Prairie-marmot is some 10 inches to one 
i nl a oO 
Fic. 235.—Long-tailed Marmot. <Avrctomys caudatus. x}. 
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 cwnicularis) and with 
tattlesnakes, all three species appearing to live in perfect amity. 
Probably the Owls use the conveniently-constructed burrows, and 
the Rattlesnakes 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 
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