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 Brtinnich’s or polar guillemot ( U. bruennichi), 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 
Brunnich’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- 
