MAMMALIA. AGT 
which are European, two Asiatic, and five African. Pl. 113, jig. 10, 
represents Myoxus glis, 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&, 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. Lach 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, C. fiber americanus (pl. 114, jig. 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 acommon 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 with mud. There are always several burrows 
along the bank, in which they seek for shelter when their huts are 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 hemisphere. Some of them have 
been considered as new generic types, and form the genera Chalicomys and 
Trogontherium, which are not universally admitted as differing sufficiently 
from the genus Castor. 
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