456 RODENTIA 
feet with five claws, that on the pollex as large as that on the fifth 
toe. Skull (Fig. 202) heavily built, with the postorbital processes 
directed outwards. Dentition (as shown in Fig. 202) remarkably 
heavy, the molar teeth 
differing from those 
of Arctomys and Sper- 
mophilus by having 
three instead of two 
transverse grooves on 
their crowns. First 
premolar nearly as 
large as the second. 
Molar series strongly 
convergent behind. 
Two species of 
Prairie Marmots, or, 
Fra. 202.—Palatal aspect of the craniuin of the Prairie Marmot as they areoften called, 
(Cynomys ludovicianus). “ Prairie - Dogs,” are 
found in North America. They live together in large communities, 
inhabiting burrows excavated at short distances apart, and feeding 
on the buffalo-grass which covers the plains. The small burrowing 
owl (Athene cuntcularia) and the rattlesnake are often found inhab- 
iting their burrows; the former probably availing itself of the 
convenience of a ready-made habitation, the latter coming there to 
feed on the young Marmots. 
Spermophilus..Size much smaller than in either of the preced- 
* ing genera; form more slender and squirrel-like. Tail very variable, 
from 1 to 8 or 9 inches in length. Cheek-pouches always present. 
Fore feet with four well-developed toes and a rudimentary pollex, 
of which the claw may be either present or absent. Skull more 
lightly built than in the other preceding genera, with the postorbital 
processes slender and directed backwards. Molar series nearly 
parallel, as in Aretomys, but all these teeth much smaller and lighter ; 
first premolar simply rounded, never more than about one-third of 
the size of the second. 
The Pouched Marmots, or Sousliks, have nearly the same dis- 
tribution as Tamias, and are represented by a considerable number 
of species. They present a far greater range of variation than 
is found among the true Marmots, some of them, such as the 
European species, being scarcely as large as a common squirrel, 
almost entirely without external ears, and with the tail reduced to 
a mere stump, barely an inch long, while others are more than 
three times this size, with large and often tufted ears, and long 
bushy squirrel-like tails. Professor Blasius gives the following 
details of the habits of the common European Souslik (8. citillus) : 
1 F, Cuvier, Mem. du Muséum, vol. vi. p. 298 (1822). 
