MAMMALIA. 467 



which are European, two Asiatic, and five African. PI. 113, fig. 10, 

 represents Myoxus rjlis.^ or fat dormouse of Europe. 



The genus Graphiurus is entirely African, and contains only two species 

 from the south and interior of that continent. The molars are remarkable 

 for their small size ; the tail is short, very fleshy. All the toes are armed 

 with pointed, compressed, arched, and strong claws. The limbs themselves 

 short, delicate, and not differing much from each other in length. 



Two or three fossil species referred to the genus Myoxus have left their 

 remains in the tertiary beds of Europe. 



Fam. 4. Castorid.e, is composed of only one living genus {Castor)^ 

 beavers. 



The genus Castor (the beaver) has very strong incisors, those of the 

 lower jaw a little smaller. In the upper jaw the molars, four in number, 

 differ slightly from each other in size, and have one internal and three 

 external grooves ; whilst in the lower one, where four also is the number, 

 there are three grooves on the inner side, and one on the external. The 

 eyes are small ; the ears short and round. Each foot possesses five toes ; 

 those of the fore feet are short and close, whilst on the hind feet they are 

 long and palmated. The tail is large, horizontally flat, and scaly. Near 

 the base of the tail exists a pouch which secretes an unctuous matter. 

 Only two species are known to belong to this genus, one in Europe and 

 another in America, G. fiber americanus {pi. 114, fig. 1), which, however, 

 resemble each other so closely that they have been pronounced identical 

 by many naturalists. 



The beavers are larger than the badger, and of all quadrupeds the most 

 industrious in constructing a common dwelling. They choose water of such 

 a depth as is not likely to be frozen to the bottom, and as far as possible a 

 running stream, in order that the wood which they cut above may be carried 

 downwards by the current to the spot where it is to be used. They keep 

 the water at an equal height, by dams composed of branches of trees, mixed 

 with clay and stone, the strength of which is annually increased, and 

 which finally, by the progress of vegetation, becomes converted into a 

 hedge. Each hut serves for two or three families, and consists of two 

 stories : the upper is dry for the residence of the animals, and the lower, 

 under water, for their stores of bark. The latter alone is open, and the 

 entrance is under water, having no communication with the land. The 

 huts are a kind of rude wickerwork, being made of interwoven branches 

 and twigs of trees plastered Avith mud. There are always several burrows 

 along the bank, in which they seek for shelter when their huts arc attacked. 

 They only reside in these habitations during the winter; in the summer 

 they separate, and live solitary. The beavers may be easily tamed, and 

 accustomed to feed on animal matters. 



Several species of the genus Castor proper have been found in a fossil 

 state in the tertiary deposits of the old hemisi^here. Some of them have 

 been considered as new generic types, and form the genera Ghalicomys and 

 Trogonthcriiim, which are not universally admitted as differing sufficiently 

 from the genus Castor. 



671 



