458 RODENTIA 
and two external enamel-folds ; the stomach has a large glandular 
mass situated to the right of the esophageal orifice; the anal and 
urethro-genital orifices open within a common cloaca; the tail is 
broad, horizontally flattened, and naked; and the hind feet are 
webbed. One or two species, Palearctic and Nearctic. 
Zoologists are not yet of accord as to whether the European 
and American Beavers should be regarded as distinct species or as 
local races; the general concensus of opinion being in favour of 
the latter view. 
The European Beaver (C. fiber) was at one time an inhabitant 
of the British Isles, having been found, according to Pennant, in 
certain Welsh rivers so late as the twelfth century, while subfossil 
remains of it occur in the peat-beds of many parts of the country. 
In Scandinavia Beavers are still found in the neighbourhood of 
Arendal. Isolated pairs are occasionally met with on the banks of 
the Rhone, Weser, and Elbe; and a considerable number are kept 
in a park belonging to the Emperor of Austria, on the banks of 
the Danube. They also occur sparingly in Russia and Poland, 
in the streams of the Ural Mountains, and in those which flow 
into the Caspian. They live in burrows on the banks of rivers, 
like the Water-Rat, and show little of the architectural instinct 
so conspicuous in the American form, but this may be owing to 
unfavourable external conditions rather than to want of the 
faculty ; for there is a well-authenticated instance of a colony of 
Beavers,-on a small stream near Magdeburg, whose habitations 
and dam were exactly similar to those found in America. 
The American Beaver (C. canadensis) extends over that part of 
the American continent included between the Arctic circle and 
the tropic of Cancer; owing, however, to the gradual spread of 
population over part of this area, and still more to the enormous 
quantity of skins that, towards the end of last and the beginning 
of the present century, were exported to Europe, numbering about 
200,000 annually, this species is in imminent danger of extirpation. 
It is distinguished from the European Beaver by the shorter and 
somewhat wider nasals. 
Remains of extinct species of Castor occur in the Pliocene of 
Europe, and in the North American Miocene; the one from the 
last-mentioned deposits being of small size, and separated by some 
writers as Lucastor. 
Extinct Genera.—A very large Beaver known as T, rogontherium 
(Diobroticus), and distinguished by the nature of the enamel-folds of 
the molars, occurs in the Upper Pliocene and Pleistocene of Europe. 
Chalicomys (Steneofiber) is a considerably smaller form from the 
Miocene of Europe and the United States, distinguished from all 
existing Rodents by the presence of an entepicondylar foramen in 
the humerus. Palwocastor, of the North American Miocene, is allied. 
