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PROCEEDINGS OE THE ACADEMY OE 
portunities for judging. While the bird is undergoing the changes incident 
to its arriving at maturity, there are great and indeed endless variations in the 
precise character of the primaries. All, however, uniformly tend towards the 
same result ; and in fully adult birds these characters are constant. 
I find no material differences in the character of the extent of the bluish 
markings of the bases of the primaries. 
The above points would seem to be sufficient to establish the position as- 
sumed, but there is another argument of a different character which, in con- 
nection with the preceding, seems quite conclusive. The Herring Gulls of both 
continents differ from the Larus glaucus, leucopterus, etc., in being essentially 
southern birds. They go north to breed only, returning again as soon as the 
duties of incubation are concluded, and moreover, do not proceed very far 
north. The American bird, at least, is found but sparingly, if at all, north of 
Cape Chidleigh, on the coast of Labrador, and is more numerous somewhat 
farther south. The Larus glaucus , leucopterus , Pagophila eburnea, etc., are 
entirely boreal birds, inhabiting the regions about the arctic circle, coming 
south only when forced to do so by the severity of winter. In view of this 
fact, it would be improper to presume upon the specific distinction of the two 
birds, unless very strongly marked and constant characters were found. 
Reasoning by analogy, it would be natural to suppose that two birds, separated 
by the breadth of the ocean, might very probably be distinct ; and discrepancies 
which in the case of truly boreal birds would be of little importance, might 
under other circumstances be of specific value.* 
In view of the above facts, I have not hesitated to separate the two birds. 
If the position assumed should be hereafter substantiated by more extended 
investigation, it will be interesting as bearing upon the law which regulates 
the identity or non-identity of birds of the two continents, which does not ap- 
pear to be as yet thoroughly understood. 
With regard to the previous comparisons which have been instituted be- 
tween the two birds, in which no differences have been discovered. It seems 
that this might have arisen in two ways. In the first place, authors who were 
impressed with the differences of the markings of the primary in the same species 
at different ages, might have considered these differences in the two species 
as equally accidental, and consequently entirely overlooked them, considering 
them as of no value whatever. The birds in other respects are so generally 
similar, that they might readily be thought identical. Again, when we are 
informed that absolutely no differences could be discovered, is it not very pro- 
bable that the European bird was compared with Northern white-tipped-pri- 
maried stype, the color of the legs not being apparent in dried skins ? For 
example : — this is certainly the case in the comparison made by Wm. Thomp- 
son, Esq. (See “ Natural History of Ireland, Birds, vol. iii. page 367, copied 
from the Proceedings of the Zoological Society of London, for 1835, page 83.) 
The comparison is here made of “six mature specimens of the Herring- 
Gull of the north of Ireland ” with the description given in the Fauna Boreali- 
Americana. As Richardson does not particularly mention the character of the 
bluish markings on the bases of the primaries, and gives the legs as flesh 
colored, there was no difficulty in referring the European specimens to the 
description. On account of the difference of size of the subterminal spot on 
the second primary of the two wings of the same individual, the author in- 
fers that “this marking is so inconstant that it should not be relied on as a 
character.” Both spots, however, were present ; and I have noticed the same 
difference in the two wings of calif ornicus, and even the presence of a minute 
white dot on the second primary of one wing of L. Smithsonianus, and its ab- 
sence from that of the other, without considering it as in the least invalidat- 
* It is due to Prof. Baird to acknowledge that the theory is not original with myself. 
[June, 
