IX.] WESTERN DIVISION. 34! 



of the western division. And here it may be mentioned in respect 

 to the two areas, that whereas many generic types of animals were 

 unable to pass from the one to the other owing to the high 

 latitude of the strip of connecting land, yet in other cases the 

 geographical limits of the range of certain genera in the Old World 

 form also an important factor in the case. As stated a few para- 

 graphs back, many of the characteristic European Plistocene 

 mammals, such as the hippopotamus, the fallow-deer, and the 

 cave-hyaena, never extended into the Asiatic portion of the Hoi- 

 arctic region, so that these and many other forms never could 

 have had an opportunity of crossing Bering Strait, even had 

 they been capable of existing in such a high latitude. 



Excluding bats and seals, the following genera of mammals 

 will be found confined to the western half of the Holarctic region, 

 although some of these range southwards into the Sonoran. There 

 are also certain genera which appear to be typically Sonoran, 

 whose range includes part of the western Holarctic region, but 

 these are best considered in the light of intruders from the 

 south l . 



Among the shrews of the western Holarctic there are two 

 species, viz. Sorex palustris, of the Rocky Mountains, and*S. hydro- 

 dromus, of Unalaska Island, which differ from all their allies in the 

 presence of long fringes of hair to the feet, although they resemble 

 ordinary species of the genus in the characters of their dentition 

 and tail. In consequence of these differences these aquatic shrews 

 have been referred by some writers to a separate genus, under the 

 name of Neosorex ; although such distinction is considered by Dr 

 Merriam unnecessary. There is, however, one genus of Insectivora 

 (Condylura), represented by the star-nosed mole, absolutely charac- 

 teristic of this area. Allied in structure and habits to the Old 

 World moles, which are totally wanting in America, this animal 

 takes its name from the presence of a star-like ring of fleshy 

 appendages at the extremity of the muzzle. 



The Carnivora include no peculiar genera 2 ; but the Rodentia, 



1 It may be well to mention here that the majority of American zoologists 

 regard as genera a number of groups to which the present writer would not be 

 disposed to grant more than sub-generic rank. 



2 Mephitis, Taxidea, etc., appear to be of Sonoran origin. 



