RODENTIA: SCIURID^;. 67 



perpetual snow, is about the size of a hare ; the color 

 yellowish-gray. It is often tamed, and is very gentle and 

 playful. 



2. Myoxinae have no post-orbital process, molars rooted, 



- , and no ccecum. 

 4-4 



The Genus Myoxus Dormice is characterized by 

 laterally compressed incisors, four grinders on each side 

 of both jaws, the crowns of which are divided by enam- 

 elled lines. Dormice are pretty little squirrel-like ani- 

 mals, of the size of rats and mice, with soft fur, hairy and 

 tufted tail, and lively eye. In the winter they become 

 torpid. So far as known, they belong to Europe and 

 other parts of the Old World. 



3. Castorinae have no post-orbital process, molars root- 

 less, , or in Aplodontia - . 



The Genus Castor Beavers is characterized among 

 all the Rodentia by the broad, horizontally flattened, and 

 scaly tail. Beavers have five toes to each foot, the hind 

 feet webbed, and the second hind toe has a double claw. 

 With one exception, they are the largest of living Rodents, 

 and are wholly aquatic in their habits ; their feet and tail 

 are admirably adapted for swimming, and their chief food 

 is bark and aquatic plants. Their incisors are very sharp 

 and powerful, enabling them to gnaw down trees of the 

 hardest wood. Beavers prefer running water, in order 

 that the wood which they cut may be carried to the spot 

 where it is to be used. They keep the water at a given 

 height by dams, which they build of trees and branches' 

 mixed with stones and mud, and build houses for winter 

 with the same materials. Each house consists of two 

 stories, and serves for two or three families. The upper 

 story is above water and dry, for the shelter of the ani- 

 mals themselves ; the lower is beneath the water, and 

 contains their stores of bark and roots. The only open- 

 ing to the hut is beneath the water. They have burrows 



