MUSEUM OF COMPARATIVE ZOOLOGY. 409 



circumpolar species. A small number of others that are properly 

 either exclusively American or Europeo-Asiatic species occur more 

 or less frequently as accidental visitors to the continents not embraced 

 within their usual habitats. 



one or another writer, and their representatives on the two hemispheres separated under 

 different names. But a considerable proportion of those mentioned in the next sub- 

 joined table are still regarded as truly circumpolar by a number of leading European 

 onithologists. Dr. Von Middehdorff (" Uebersicht der Natur Nord- und Ost-Sibiriens, 

 Theil 2, Erste Lieferung," etc.; see Newton's Ibis, April, 1870, p. 275), in 1867, gave 

 lists of eighty-seven circumpolar species, a part of which (called " Hyperboreal Birds ") 

 are distinctive of what has been termed above the Arctic Realm, whilst many of the 

 others range quite far southward even in summer. These lists, however, do not era- 

 brace a number of circumpolar species whose boreal limit does not extend to the 

 districts named. A dozen or more Europeo-Asiatic species, in addition to those given 

 below, have representatives in America so closely resembling them in habits and in 

 geographical distribution, as well as structurally, that they have often been confounded, 

 specimens frequently occurring on the one continent that are undistinguishable from 

 those from the other continent. 



In 1846 Professor Edm. de Selys-Longchamps, in his excellent paper entitled " Sur 

 les Oiseaux americains admis dans la Faune europeenne " (Mem. de la Soc. R. de Liege, 

 Vol. IV, pp. 35-50, 1849), included thirteen species in his list of " Oiseaux terrestres 

 communs a 1'Europe et a l'Amerique," and mentions nine other terrestrial American 

 species which he regards as "ne semblent etre en realite que des modifications clima- 

 tiques de nos oiseaux europeens." All but two of these, and also one or two in addi- 

 tion to them, have been regarded in the present paper as specifically identical. In his 

 list of" Oiseaux aquatiques communs a. 1'Europe etal'Amerique " he includes fifty-five 

 species, and mentions thirteen others, " decrits comme especes distinctes, ne semblent 

 etre que des races locales," three or four of which I have regarded as specifically iden- 

 tical. The whole number mentioned by Selys-Longchamps as common to Europe and 

 boreal America is seventy-six, plus twenty -four " autres qui semblent n'etre que des 

 races legerement modifiees par le climat." (See 1. c, p. 48.) In the same paper he gives 

 a list of twenty-eight American species as of accidental occurrence in Europe, eight of 

 which are land birds, eight echassiers or waders, and twelve palmipedes or swimmers, 

 and also a list of twenty American species which he considers to have been improperly 

 included among the birds of Europe, among which are HaUaetus leucocephalus, Slrix 

 nebulosn (= Syrnium nebitlosum), Loxia{= CurvirOstra) leucoptera, Struihus (= Junco) 

 hyemalis, and Parus (= Lophophanes) bicolor. 



