187S.] MR. H. SAUNDERS ON THE LARINiE. 163 



strongest evidence against it is that brought by Dr. Coues in his 

 ' Birds of the North- West, ' p. 646, where he says that whereas " a 

 part of the Kittiwakes from the North Pacific are not distinguishable 

 in any way from the North-Atlantic bird, others have the hind toe as 

 perfectly formed and proportionately as large as in any species of 

 Larusl And there is a gradation between them." He goes on to 

 cite an extreme example from Plover Bay, with a hallux, including 

 the nail - 2 in., with a perfect claw. Whilst writing this paper I have 

 received, through the kindness of the authorities of the Smithsonian 

 Institution at Washington, a similar extreme form with a hallux and 

 nail - 2 in., the claw being well formed and curved, although the whole 

 is certainly but small for the size of the bird, as may be seen by a com- 

 parison with a species of about the same size, L. canus, in which the 

 hallux and nail measure '5 in. Mr. O. Salvin has also lent me two 

 specimens, both, as well as my own, from Alaska, in the one of 

 which the nail is somewhat less developed, whilst in the other it 

 is absent, as in the Atlantic bird. It is probable that this ex- 

 treme form is both rare and local ; at least I have never been able to 

 find any but these two examples amongst the many Kittiwakes, 

 Pacific and others, which I have examined. However, there it is; and 

 if the genus Rissa depended solely upon the absence of the hind toe, 

 it would have to be given up. There are, however, other structural 

 characteristics, which, when united, seem to me to have weight. The 

 tarsus is remarkably short, being only 1*2 against 1*9 in. in length 

 of middle toe and claw, proportions unknown in any other group of 

 Gulls ; the shape of the curved bill is also peculiar ; the tail is visibly 

 although not deeply, forked ; whilst these structural differences are 

 supplemented by such minor characteristics as the peculiar livery of 

 the immature bird, totally unlike that of the adult, or of the young 

 of any other species, and by its exclusively crag-nesting habits. Bear- 

 ing all these points in mind, I think that, although it is no longer 

 absolutely correct to say that the genus Rissa depends upon the 

 absence of the hallux, yet it is advisable to retain it as, on the whole, 

 a valid natural division, sanctioned, moreover, by general use during 

 upwards of half a century. 



2. Rissa tridactyla (Linn.). 



Larus rissa, Linn. Syst. Nat. i. p. 224 (1/66); Phipps, Voy. 

 N. Pole, App. p. 18/ (1774) ; Leach, Syst. Cat. Brit. Mus. p. 40 

 (1816); Scoresby, Arct. Voy. i. p. 534 (1820). 



Larus tridactylus, Linn. Syst. Nat. i. p. 224 (1766) ; 0. Fabr. 

 F. Groenl. p. 98 (1780) ; Gm. Syst. Nat. i. p. 595 (1788); Schl. 

 M. P.-Bas, Lari, p. 31 (1863) ; Godman, Ibis, 1872, p. 222 (Ca- 

 naries). 



Larus albus, P. L. S. Mviller, Natursystem, p. 108 (1776) (based 

 on Buffon's Mouette cendree tachetee). 



"Larus cinerarius, Linn." O. Fabr. F. Groenl. p. 101 (17S0), nee 

 Linn, (winter-plumage, from description). 



Larus riga (mispr.), Gm. Syst. Nat. i. p. 594 (1788). 



Larus ncevius, Schaff. Mus. Orn. p. 64 (1789). 



[9] 



