_Gavia arctica suschkini_ (Sarudny) 5 males from Turkestan, average, bill 2.35 wing 12.40 largest, " 2.60 " 13.35 smallest, " 2.20 " 11.80
_Gavia arctica arctica_ (Linnæus) 6 males from Europe, average, bill 2.44 wing 12.24 largest, " 2.62 " 12.75 smallest, " 2.30 " 12.
_Gavia arctica viridigularis_ (Dwight) 4 males from Bering Sea region, average, bill 2.63 wing 12.69 largest, " 2.87 " 13. smallest, " 2.50 " 12.
The other characters are equally confusing. The nape is lightest and almost constantly so in North American _pacifica_; it is darkest in _viridigularis_ and more or less intermediate in many specimens of the other two forms.
The black throat patch terminates below in a straight line almost invariably in North American _pacifica_; I have seen but one exception to this rule; but in Siberian _pacifica_ this character is less constant. In _viridigularis_ this patch terminates below in a decided point, in all specimens that I have seen. In European _arctica_ about half of the specimens I have seen have the patch decidedly pointed below and the others have it nearly straight or only slightly pointed.
The colored reflections of the black throat-patch are the most variable and inconstant of all the characters. In _viridigularis_ three of the specimens examined show mainly greenish colors but even these show some signs of purple; and in one, a bird in my own collection, the colors are about equally divided. In European _arctica_ about half of the specimens show mainly purplish reflections, while fully half show both purplish and greenish. In North American _pacifica_ the purplish reflections predominate, but five specimens out of twenty-two show more or less greenish in certain lights. Mr. Waldron DeWitt Miller, in sending me descriptions of Pacific Loons in the American Museum, used the following terms in designating the colors of the throats; greenish-blue, bluish-green, dark greenish-blue, violaceous and dark violet. It can be easily seen from the above that the colors are very variable.
Dr. Dwight says, in his diagnosis of _viridigularis_:—“The green coloration of the throat is the essential character that sets this species apart from _arctica_ and its races, which all have purple throats.” In the light of the facts stated above this “essential character” disappears and his new species must be reduced to the rank of a subspecies at least. Even a subspecies must prove to be fairly constant in a more or less definite range. The range of _viridigularis_ is very imperfectly known; the four specimens, referable to this form, that I have seen were taken at Nijni Kolymsk, Siberia, St. George Island, Bering Sea, Nome and Saint Michael, Alaska; Dr. Dwight’s specimens all came from northeastern Siberia. The Nijni Kolymsk bird, referred to above, is somewhat intermediate between _viridigularis_ and _arctica_; if it had been taken in Europe it would probably be referred to the latter. I also have a perfectly typical _pacifica_ from the Kolyma River, Siberia.