AUKS. 



535 



of the North Pacific is the largest representative of the second modification of the 

 group, in which the beak is much shorter and deeper than in the preceding, while 

 the nape of the neck and back of the head are black like the back. A portion of 

 the base of the cutting-edge of the mandible is light-coloured. Finally, we have 

 the so-called Briinnich's or polar guillemot ( U. hruennichi), of the North Atlantic 

 and Arctic Oceans, in which the size is smaller, and the whole of the cutting-edge 

 of the upper mandible yellowish white. Mr. Seebohm considers, however, that 

 Briinnich's guillemot is so inseparably connected by the Californian form with 



COMMON GUILLEMOTS (J nat. size). 



the common guillemot, as to render it impossible to regard them as more than 

 varieties of a single species. Whatever diversity of opinion may obtain as to the 

 distinctness of the above-mentioned forms from the common guillemot, there can 

 be none as to that of the black guillemot ( U. grylle), which is referred, indeed, by 

 some writers to a separate genus. It is a smaller bird than the common guillemot, 

 from which it is at once distinguished by the whole of the under-parts being black 

 in the summer dress ; the beak being relatively short. Typically an inhabitant of 

 the North Atlantic, it is represented in the circumpolar seas by a variety dis- 

 tinguished by the larger size of the conspicuous white patch on the wings. In 

 the North Pacific it is replaced by the pigeon-guillemot ( U. columba), character- 



