298 PROCEEDINGS OF THE ACADEMY OP 



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 markiner 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 californicu*, and even the presence of a minute 

 white dot on the second primary of one wing of L. Smithtonianus, 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, 



