of Colymbus adamsi in Norway. 279 



the neck-bar is broader than the collar. The neck-bar in 

 C. adamsi is acutely pointed in front and behind, and its 

 greatest width is at the middle, whilst in C. glacialis it is 

 widest behind, and terminates there with almost parallel 

 sides. 



Finally, the neck-bars in C. adamsi are separated in front 

 by a space which is about equal to its greatest width, whilst 

 in C. glacialis they are almost confluent in front. 



(7) The Dots on the Back. 



The white dots on the back are comparatively and abso- 

 lutely larger in C. adamsi, and are contained not quite 

 twice, but as a rule once and a half, in the width of 

 the neck-bar. Thus the largest spots in the specimen 

 in nuptial plumage (from Balsfjord) are of a length of 19 

 mm., the neck-bar is 34 mm. wide. In C. glacialis the 

 relationship is often as 1 to 3 or 4, more rarely as 1 to 2. 

 Some authors have pointed out another character in the 

 number of spots, which, however, appears to be of little 

 value. Their number on the fore part of the back and 

 scapulars is hardly less in C. adamsi than in C glacialis 

 {cf. Stejneger, Nyt Mag. f. Naturv. xxvii. p. 121). Coues 

 {' Birds of the North -West,' p. 720) points out a difference 

 in their shape ■'^. This character, however, is likewise 

 variable. 



(8) The Colour of the Throat and Neck -collars. 



In C. adamsi the front of the upper collar and the whole 

 of the lower (broad) collar are bluish black with a strong 

 violet gloss t, which, however, is absent on the whole of the 

 upper part of the head and on the back of the neck. The 

 boundary where the blue gloss ceases on the sides is sharply 

 defined, and there thus arise indications of a separately- 

 coloured portion, which corresponds to the black throat of 

 C arcticus and the red of C. septentrionalis. 



* " White spots of back nearly square " in C. i/lacialk (Coues, I. c). 

 t This is of coui^e most observable iu the full nuptial plumage. 



