406 BRITISH BIRDS. 



of its plumage^ but may be distinguished at all seasons o£ the year by its 

 large ivory-coloured bill. In summer plumage the forehead, erown, and nape 

 are glossed -with green, and the chin, throat, and lower neck all round with 

 purple ; the white spots on the scapulars arc larger than in the allied species, 

 whilst the spots on the flanks and upper tail-coverts are smaller. The 

 most important distinction is to be found in the number of white streaks 

 in front of tlie throat and on each side of the neck. Of the former there 

 are six in C. adamsi and twelve in C. glacialis ; whilst of the latter there 

 are ten in C. adamsi and eighteen in C. (jlaciuUs. It is a sliglitly larger bird 

 than the Great Northern Diver, having on an average a decidedly larger 

 bill, measuring from the frontal feathers to the tip from 3i to 3| inches, 

 that of the Great Northern Diver only measuring from 2f to 3^ inches. 

 Compared with the bill of the Great Northern Diver, it appears to be 

 slightly recurved, an effect produced by the straightncss of the culmen, 

 which in the Black-billed species is decidedly decurved. Legs and feet 

 olive -brown ; iridcs light hazel. In the changes of its plumage it resembles 

 its ally. 



