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 Ardomys and Sp&r- 

 mophilas 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, 



Fig. 202. — Palatal aspect of the cranium of the Prairie Marmot ft g the V are of ten Called 

 (Cynovujs ludovicianus). u p^^ _ j^,, ^ 



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 cunicularia) 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. 



Spermojjhihcs. 1 — 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 Ardomys, 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 (S. citillus) : 

 1 F. Cuvier, Mem. du Museum, vol. vi. p. 293 (1822). 



