<><) Mcrr LCI in Geographic Distribution of Life. 



and climate," he admits, u and the two so closely approach each 

 other at Bering Strait, that we cannot wonder at there being a 

 certain amount of similarity between them a similarity which 

 some naturalists have so far overestimated as to think that the 

 two regions ought to be united.' 1 After enumerating a number 

 of mammals common to the two he goes on to say: "We un- 

 doubtedly find a very close resemblance between the two regions, 

 and if this were all, we should have great difficulty in separating 

 them. But along with these we find another set of mammals, 

 not quite so conspicuous but nevertheless very important. We 

 have first, three peculiar genera of moles, one of which, the star- 

 nosed mole, is a most extraordinary creature, quite unlike any- 

 thing else. Then there are three genera of the w r easel family, 

 including the well-known skunk (Mephitt*), all quite different 

 from eastern forms. Then we come to a peculiar family of car- 

 nivora, the raccoons, very distinct from anything in Europe or 

 Asia ; and in the Rocky Mountains w r e find the prong-horned 

 antelope (Antilnrapra) and the mountain goat of the trappers 

 (Aplocerus [= Mazanici]), both peculiar genera. Coming to the 

 rodents, we find that the mice of America differ in some dental 

 peculiarities from those of the rest of the world, and thus form 

 several distinct genera ; the jumping mouse ( Xuptiy [-- Zti.pus]) 

 is a peculiar form of the jerboa family ; and then we come to the 

 pouched rats ( Geomyidfe), a very curious family consisting of 

 four genera and nineteen species, peculiar to North America. 

 though not confined to the Nearctio region. The prairie dogs 

 (Ci/nomyii), the tree porcupine (Eirfhizttii), the curious sewellel 

 (Haploodon [==Aplodontlci\}, and the opossum (Didelphis) com- 

 plete the list of peculiar mammalia which distinguish the north- 

 ern region of the new world from that of the old." (Island Life, 

 ]>. 48.) 



As already shown in an earlier part of the present essay, most 

 of these genera and several of the families belong to the austral 

 or Sonoran region and have no place in the Boreal fauna the 

 only one that can be compared with the fauna of northern 

 Eurasia. As a matter of fact, 81 genera of non-pelagic mammals 

 are now recognized in ' extratropical ' North America the so- 

 called Xearctic Region. Of this number 41 are found in no other 

 part of the world.*' These genera are enumerated in the follnw- 



The intrusive genera />///<//>// /*, Ttu^<i, Dicoiijlrx, /Vor//o//, AW.sv/^, and 

 lnxxti* which are clearly of South American oriirin, are not liere included. 



