Species of Phylloscopus. 263 



according to colour, while the first-mentioned has the size of 

 the former, and the two others are not larger than ordinary 

 Ph. borealis. Henson^s no. iv (Hakodate, Japan), on the 

 other hand, belongs to the last-mentioned form by its general 

 size and the first primary, while it is coloured like Ph. 

 xanthodryas. Henson^s no. y (Hakodate) is a Ph. xantho- 

 dryas by its size, a Ph borealis by its colour, with the first 

 primary intermediate. U. S. Nat. Mus. no. 96254 (Blakist. 

 no. 1879 ; Hakodate) is also a Ph. xanthodryas by size and 

 partly by its colour, but its first primary does not reach 

 beyond the longest primary- coverts. The result is that if 

 you arrange your birds in two groups according to either one 

 of the three diagnostic characters, the two gronps will contain 

 different specimens every time. 



" It cannot be denied, however, that there is a general 

 tendency in the larger birds to have a proportionally larger 

 first primary and a yellower tint, and it may be that this 

 tendency would be more striking were all the specimens 

 properly sexed. It is also somewhat significant that we find 

 none of the Ph. xanthodryas style in the Alaskan series. It 

 is furthermore clear from the dates of the different birds that 

 season has nothing to do with the intensity of the yellow 

 colour. I am therefore not prepared to give up Ph. xayitho- 

 dryas entirely, but as intermediate specimens undeniably 

 occur, I shall at least provisionally adopt the course indicated 

 by me on a former occasion (Res. Orn. Expl. Kamtsch. 

 p. 306), calling the yellow biixl Ph. borealis xanthodryas, in 

 spite of the fact that it is difficult at present to assign a 

 definite habitat to the two forms, as both seem to occur in 

 the same countries. It is possible, however, that Ph. 

 xanthodryas is the breeding bird of Japan, and that Ph. 

 borealis only occurs there on the migrations ; this is a question 

 for the resident ornithologists there to investigate and solve.'' 



That only P. borealis occurs in Siberia and in Alaska, to 

 me proves a good deal ; it proves, I think, specific dis- 

 tinctness. 



From Stejneger's account of the specimens compared, I am 

 not satisfied that all his so-called examples of P. xanthodryas 



T 2 



