MUSEUM OF COMPARATIVE ZOOLOGY. 401 



and to the intervening islands, constituting a distinct fauna, which 

 may well be called the Aleutian Fauna. Tlie mingling of Asiatic 

 and American species forms its distinctive feature. There is also a 

 slight commingling of western species in the valley of the Mac- 

 kenzie's River, as there is also in the valley of the Saskatchewan. 

 The Hudson ian Fauna doubtless embraces outlying islands in the 

 Canadian Fauna, as the upper part of the White Mountains, and the 

 summits of some of the higher peaks of the Adirondacks. The 

 southern point of Greenland embraces many species common to the 

 Hudsonian Fauna, and though Greenland belongs almost wholly to the 

 Arctic Realm, its extreme southern portion is doubtless Hudsonian.* 



The Hudsonian Fauna being coextensive northward with the limit 

 of forest-trees, it forms the northern limit of distribution of all the 

 species of birds whose mode of life renders them dependent upon a 

 forest vegetation. The distinction between the Hudsonian Fauna and 

 the Arctic Realm, as well as between the Temperate Realm and the 

 Arctic Realm, is hence a strongly marked one, nearly one hundred 

 species, nearly all of them land birds, finding their northern limit of 

 distribution near the polar limit of forests, or at least within the Hud- 

 sonian Fauna. 



The Huds.cnian Fauna may be distinguished from the Canadian by 

 the absence of the species given in the preceding lists and by the 

 presence of those enumerated in the first of the lists next subjoined, 

 and from the Arctic Realm by the presence of those given in the 

 second list below. 



1. Species limited by the Hudsonian Fauna in their Southward Range in the 

 Breeding Season. 



1. Anthus ludovicianus. 9. . ?Picoides arcticus. 



2. Saxicola oenanthe. 10. ?Picoides hirsutus. 



3. Ampelis garrula. 11. Faleo candicana. 



4. JEgiothus linaria. 12. Archibuteo lagopus. 



5. Plectrophanes lapponicus. 13. Syrnium cinereum. 



6. Plectrophanes nivalis. 14. Nyctea nivea. 



7. Plectrophanes pictus. 15. Lagopus albus. 



8. Leucosticte tephrocotis. 16. Lagopus rupestris. 



* For remarks respecting the similarity of the Fauna of Northern Labrador and 

 Southern Greenland, see Dr. A. S. Packard, Proc. Bost. Soc. Nat. Hist., Vol. X, p. 255, 

 1866. 



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