360 GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION. 



restricted to the parks and plains of the Rocky Mountain plateau 

 region. 



The remaining sciuromorphs comprise the sewellels (Haplodon), 

 leporine rodents, somewhat of the habit of the musk-rat, inhabit- 

 ing the Northwestern United States ; the singular anomalures from 

 Western Africa, which, in the possession of a lateral cutaneous 

 expansion adapted to aerial sailing, recall the fly ing- squirrels ; 

 and the beavers (Castoridae), of which the only species (Castor 

 fiber or Canadensis) inhabits the northern parts of both the East- 

 ern and Western Hemispheres. In its American home the beaver 

 is still met with in tolerable abundance west of the Mississippi 

 in the entire tract included between Alaska and Mexico ; to 

 what extent its range extends into the last-named country has 

 not yet been ascertained. East of the Mississippi it is now but 

 sparingly found south of the Great Lakes, a limited number being 

 still harboured in the Maine and Adirondack wildernesses, and a 

 still smaller number probably finding their way along the thinly 

 settled districts southward to Alabama and Mississippi. In some 

 portions of Virginia and Pennsylvania they appear to be still fairly 

 numerous. The present range of the beaver in Europe is even 

 more restricted than in America, the animal being almost wholly 

 confined to Russia (and Poland), specially the streams of the Ural 

 Mountains and those emptying into the Caspian Sea, and, in iso- 

 lated colonies, to the Rhone, Weser, Elbe, and Danube rivers. 

 The animal is now extinct in Great Britain, and appears, also, to 

 have completely disappeared from Scandinavia. 



The hystricomorphs embrace a number of families whose repre- 

 sentatives depart widely from one another in many essential char- 

 acters ; their greatest development is in the Neotropical realm, 

 which alone possesses the chinchillas, the agoutis, and the cavies, 

 besides the greater number of the partially Ethiopian family of 

 spiny-rats (Echiomyida3). The best-known representative of the 

 last is the coypu (Myopotamus coypu), a large beaver-like animal 

 found only in Chili, measuring nearly two feet in length. Of scarcely 

 smaller dimensions is the arboreal Capromys pilorides, indigenous 

 to Cuba, where it constitutes the largest native mammalian. Pla- 

 giodontia aedium, a member of the same family, also found in San 

 Domingo, appears to be the only indigenous mammal of the island of 

 Jamaica, except the bats and mice (the latter probably introduced). 



