FAUKA OF THE HOLAECTIC EEALM. 65 



Thomomys, 1 pouohed-rats or -^Plocerus, the Rooky Mountain 

 Dipodomys, gophers. 8°^*- 



Perognathus, J Procyon, the raccoon. 



Jaculus, the jumping-mouse. Mephitis, the skunk. 

 Fiber, the musk-rat. Latax, the American otter. 



Cynomys, the prairie-dog. 

 Erethizon, the Canadian porcu- 

 pine. 



Common to both divisions : 



Lagomys, the pika. Bison, the bison. 



Arctomys, the marmot. Rangifer, the reindeer. 



Spermophilus, the pouched-mar- Alces, the elk. 



mot. Thalassarctos, the polar bear. 



Castor, the beaver. Gulo, the glutton. 



Myodes, the lemming. Lyncus, the lynx, and most of the 

 Arvicola, the field-mouse. seals and the walruses. 



Ovis, the sheep. 



The bird-faunas of the Old and New World divisions of the 

 Holarctic tract differ very materially from each other, a condi- 

 tion in great measure explained by the circumstance that in both a 

 large representation is obtained through migration from extra- 

 limital regions. Thus, the Eurasiatic or Palsearotio avifauna is 

 largely made up of types which are equally Ethiopian or Oriental ; 

 and in like ma,nner a very large proportion of the similar North 

 American fauna is made up of forms which might with equal 

 justice be considered Neotropical or Nearctic. But even in the 

 case of the resident birds, or such as may be considered to be more 

 properly belonging to the region, marked difEerences, sufficient to 

 characterise the two divisions, present themselves. The prepon- 

 derating Eurasiatic forms belong, among the perchers, to the 

 families of thrushes (Turdidse) — with the cosmopolitan genus Tur- 

 dus; warblers (Sylviadse), with the true warblers (Sylvia), red- 

 start, robin, and nightingale (Luscinia); nuthatches (Sittidae), tits 

 (Pai-idee), Muscicapidse (Old World fly-catchers), shrikes (Laniidae), 

 crows (Corvidse), with the pies, crows proper, and jays ; swallows 

 (Hirundinidae), finches (Fringillidae) — gold-finch, haw-finch, cross- 

 bill, bull-finch, linnet, sparrow, grosbeak, lark-bunting, true finch 

 6 



