Vol 'i XXXV ] Oberholser, Subspecies of Larus hyperboreus. 467 



subspecies of Acanthis linaria, because it intergrades perfectly 

 with that species, but not with Acanthis hornemanni. While of 

 course in some plumages certain specimens are difficult to dis- 

 tinguish, the same is true of many another distinct species. Pres- 

 ent comparisons, based on specimens in breeding plumage, show 

 that Acanthis hornemanni exilipes and Acanthis linaria linaria are 

 usually separable by the white rump and the slight streaks on the 

 under tail-coverts of the former, which are the characters that ally 

 Acanthis hornemanni exilipes to Acanthis hornemanni hornemanni; 

 in fact, in ordinary condition Acanthis hornemanni exilipes is a 

 miniature of Acanthis hornemanni hornemanni, though it averages 

 somewhat darker. A further and serious obstacle to considering 

 Acanthis hornemanni exilipes a subspecies of Acanthis linaria 

 linaria is that both breed on the same ground over a wide geo- 

 graphic area extending from Ungava to southern Keewatin and 

 Alaska, and that they retain their distinctive characters every- 

 where, although apparently sometimes hybridizing. It is evident, 

 therefore, that whatever the relationship of Acanthis hornemanni 

 exilipes to Acanthis hornemanni hornemanni, the former cannot 

 by any means be a subspecies of Acanthis linaria. 



THE SUBSPECIES OF LARUS HYPERBOREUS 

 GUNNERUS. 



BY HARRY C. OBERHOLSER. 



No subspecies of Larus hyperboreus have hitherto been formally 

 recognized. Recent investigation, however, has shown that the 

 bird of Alaska, described by Mr. Ridgway as Larus barrovianus, is a 

 readily separable race. Its relationships with Larus hyperboreus 

 hyperboreus are set forth below. 



For the purpose of the present study the writer has been priv- 

 ileged to examined 240 specimens, including the type of Larus 

 barrovianus, which number represents the entire material of this 



