CASTORIDAE 457 
“Tt 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 Russian 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 Arctomys 
and Seiwrus, but with tritubercular upper molars and no postorbital 
processes to the skull; in the latter respect agreeing with the next 
family. In the size of the preorbital vacuity the skull resembles the 
Hystricomorpha. 
Family HAPLODONTID&. 
Distinguished from the Sciwride hy the absence of postorbital 
processes to the frontals, the depressed skull, and the rootless cheek- 
teeth. Premolars ?; the penultimate upper one small. 
Haplodon1—H. rufus and H. inajor, of North America, west’ of 
the Rocky Mountains, are the only representatives of the family; 
their habits are similar to those of Cynomys. 
Family CASTORIDE. 
Skull massive, without postorbital processes, the angle of the 
mandible rounded, and the cheek-teeth rootless, with re-entering 
enamel-folds. Premolars +. Habits natatorial. 
Castor.2—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). 
