60 Mcrrlaiii — Geographic Didrihiitlon of Life. 



and climate," he admits, " and the two so cdoselv a[)i)i'uach 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 tar overestimated as to think that the 

 two regions ought to be united."" After enumerating a number 

 of mamiiials cummon to the two he goes on to say: "We un- 

 doubtedly tind 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 mannnals, 

 not ([uite sd conspicuous l)ut nevertheless very important. We 

 have tirst, 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 weasel family, 

 including the well-known skunk (Mephitix), 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 Rock}'- ^Fountains we tind the prong-horned 

 antelope (Antilocapra) and the mountain goat of the trappers 

 (Aplocerus [=M(izain(i']), both peculiar genera. Coming to the 

 rodents, we tind 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 ( Xapas \_= ZapuxJ) 

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

 |:)0uched rats i Geoini/ichf.'), a very curious family consisting of 

 four genera and nineteen species, peculiar to North America, 

 though not confined to the Nearctic region. The prairie dogs 

 {C;jni)iiij/.s)^ the tree porcupine (Erethizoii), the curious sewellel 

 (Hapl()()(h)ii \_=Apl(i(hiiiti(i^)^ and tlie oi)ossum (Didelphi.s) com- 

 plete the list of peculiar mammalia Avhich distinguish the north- 

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

 p. 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 liiuna — the 

 only one that can be compared Avith the fauna of northern 

 luirasia. As a matter of fact, 81 genera of non-2)elagic mammals 

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

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

 l)art of the world.* These genera are enumerated in the follow- 



"" The intrusive genera Didcl/ihlx, Taivxhi. Diroti/lt.^t, Prori^oti, Na.'^iia, and 

 J/y/yxs«s, wliifh are clearly ofSuutli American origin, are not liere included. 



