248 ON THE DIFFERENT SPECIES OF 
mere examination and comparison of specimens, and, still 
more so, by attempting to refer them to the species esta- 
blished by naturalists. 
My object being to exhibit the subject in as clear a light 
as possible, I shall, in the first place, give a short but cir- 
cumstantial account of the genus considered individually, 
and then proceed to the particular species. But previous 
to this, it will be proper to observe, that the paper, such as 
it is, owes its existence to Professor Jameson, who, aware 
of the uncertainty that prevails in this very interesting ge- 
nus, wished me to attempt its elucidation. The specimens, 
which have furnished the principal materials of this neces- 
sarily imperfect memoir, form part of the splendid collec- 
tion of birds in the Museum of the University ; the de- 
scriptions are in all cases taken from actual specimens, and 
the specific characters elaborated without any reference to 
those of authors. For the variations exhibited in the young 
birds, as well as information on other points, I have trusted 
implicitly to Temminck and Montagu: wherever infor- 
mation has been derived from other sources, it will be faith- 
fully acknowledged. 
Larus, Gull, 
Natural Generic Character. — Beak of moderate length, 
straight, compressed, the sides rounded, the edges bent in- 
wards and sharp ; the upper mandible declinato-incurvate 
at the end, sharpish ; under mandible forming a prominent 
angle near the end, at the junction of its crura, obliquely 
truncate and grooved internally at the tip. 
Nostrils lateral, mesial, longitudinal, linear, with the fore- 
end rounded, open, perforated. 
