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mandible, described above, is white, and presents a very conspicuous 

 feature ; the slate of the head and hind-neck is darker, and with a 

 more distinct shade of bluish ; the brown of the fore-neck and throat, 

 with its edge more distinctly defined and bounded nearly by a line 

 which, starting from the anterior extremity of the nasal furrow, runs 

 down the neck, passing immediately below the eye and encroaching 

 somewhat on the nape ; the tongue of white, running up the fore- 

 neck, is quite conspicuous. Tip of bill yellowish horn-color. Win- 

 ter plumage generally similar to that of trollle, but with the dark 

 color descendino- lower. White of the throat and fore-neck much 

 less extended, and not so distinctly separated from the dark color ; 

 the anterior extremity of the chin is dusky, and the white does not 

 rise higher than a line, which, starting from the rictus, runs directly 

 backwards ; the brown of the lower part of the throat is only nar- 

 rowly separated by white, marking very plainly the outline of the 

 summer plumage of that part. The plumage of the young in winter 

 resembles precisely that of the adult ; the bill is, however, quite dif- 

 ferent, being much more slender and compressed, and the bare edge 

 of the posterior mandible darker and much less conspicuous. In the 

 downy plumage the colors are disposed in precisely the same manner 

 as in the winter plumage, with the same white bristly terminations 

 to some of the downy feathers on the hind-neck, already described in 

 the same plumage of U. troille. The bill is very short and slender, 

 and hardly differs from that of the other species at the same age. 

 According to Naumann it can then only be distinguished with great 

 difficulty from the very young Alca torda. Having never seen speci- 

 mens of the latter bird in this plumage, I have not been able to com- 

 pare the two. Gould, however, states that the white line from the 

 bill to the eye, so conspicuous in the full-plumaged adult, is plainly 

 visible in the downy plumage, though it disaj^pears in the fully 

 fledged young. As the scutellation of the tarsi of the two genera is 

 very unlike, it seems to me that there can be no difficulty in distin- 

 guishing them. European specimens from the Orkneys have the 

 same general appearance, the bill not quite so stout and the plumage 

 faded and worn. A specimen from the Herald Island, Arctic Ocean, 

 resembles the European specimens in the lighter color of the plumage, 

 but the bill is stouter. The Greenland specimens are in fine plumage 

 and the bill appears rather stouter even than in those from Labrador, 

 but the cutting edge of the posterior part of the upper mandible is not 

 so prominent or sharp as in the specimen described ; in one of them it 

 is yellow and semitransparent, as if it had been rubbed with oil. This 

 color corresponds with Briinnich's description, " cujus margines etiam 

 in exsiccatis exuviis Jlavescunt." I have never seen any appearance 

 of yellow in any other specimen ; the white resembles more an 

 efflorescence of some white salt, on a dark surface, than any thing 



