CASTORJD^E 457 



" It lives in dry treeless plains, especially on a sandy or clayey soil, 

 and is never found either in forests or on swampy ground. It 

 forms burrows, often 6 or 8 feet deep, in which food is stored up 

 and the winter sleep takes place. Each burrow has but one 

 entrance, which is closed up when winter approaches, a second 

 hole, however, being previously formed from the sleeping-place to 

 just below the surface of the ground. The second hole is opened 

 the next year, and used as the ordinary entrance, so that the 

 number of closed-up holes round a burrow gives an indication of 

 the length of time that it has been occupied. Sousliks ordinarily 

 feed on roots, seeds, berries, etc., but occasionally also on animal 

 food, preying readily on eggs, small birds, and mice, the remains of 

 these latter being often found in their burrows. They bring forth 

 in the spring from four to eight young ones, which, if taken early, 

 may be easily tamed. They are often eaten by the peasants, the 

 inhabitants of the Eussian steppes considering their flesh an 

 especial delicacy." 



Remains of Spermophilus are not uncommon in European Tertiary 

 deposits, some belonging to living and others to extinct species. 



Extinct Genera. Plesispermophilus, from the Upper Eocene Phos- 

 phorites of Central France, appears to be closely allied to the 

 Sousliks. Plesiarctomys (Sciuravus or Paramys), which is common 

 to the Middle Tertiaries of Europe and North America, appears to 

 be a generalised form, showing some resemblance both to Ardomys 

 and Sciurus, but with tritubercular upper molars and no postorbital 

 processes to the skull ; in the latter respect agreeing Avith the next 

 family. In the size of the preorbital vacuity the skull resembles the 

 Hystricomorpha. 



Family HAPLODONTID.E. 



Distinguished from the Sciuridce by the absence of postorbital 

 processes to the frontals, the depressed skull, and the rootless cheek- 

 teeth. Premolars f ; the penultimate upper one small. 



Haplodon. 1 H. rufus and H. major, of North America, west of 

 the Rocky Mountains, are the only representatives of the family; 

 their habits are similar to those of Cynomys. 



Family CASTORID^E. 



Skull massive, without postorbital processes, the angle of the 

 mandible rounded, and the cheek-teeth rootless, with re-entering 

 enamel-folds. Premolars y. Habits natatorial. 



Castor? The upper molars are subequal, each with one internal 



1 Richardson, Zool. Journ. vol. iv. p. 334 (1829). Amended. 

 2 Linn. Syst. Nat. 12th ed. vol. i. p. 78 (1766). 



