specie sqf the Genus Lams, or Gull Tribe. 171 
lation of the species from some obscure property in themselves, 
or from the name of the discoverer, they were to be taken from 
Some obvious and discriminating external character. 
In both the black and white species the irides are hazel- 
brown, and the legs and feet black. The bill is dusky black, 
and about an inch and a half longv from the cheek to the point 
of the upper mandible, which is composed of two pieces. The 
outer piece is horny and hooked at the point, and is overlapped 
by that which proceeds from the base. This overlapping piece, 
when removed, leaves a bluish vascular membrane below it, in- 
to which the hooked and anterior piece is inserted. The nos- 
trils are linear, and appear like lateral slits at the place of junc- 
tion of the two pieces of the bill. The under mandible is 
straight, and has a projection downwards near to the point. 
By attending carefully to these circumstances, and to the 
general description, the two kinds of Arctic gull may be readily 
distinguished from each other. The mistake of confounding 
them together, seems to have arisen from the circumstance, that 
the first description was taken from a male of the white, and a 
female of the black species, and succeeding naturalists, instead 
of examining for themselves, have been satisfied with the dis- 
tinctions which they received. 
But the 'most important fact in the history of the Arctic gull is, 
that the young bird, in its progressive stages, until it has at- 
tained the perfect plumage, is the Lards crepidatus of Linnaeus ; 
the Stercoraire of Brisson, the Lesbbe a courte queue of Cuvier, 
and the Black-toed Gull of Pennant and other British ornitho- 
logists. This I have ascertained to be true, from having traced 
the yotmg ones from the time they came out of the shell, until 
they had acquired the size, vigour, and habits of the parent 
gulls. They differ sensibly from each other, even when only 
a month old, according as they are descended from the black 
or the white species ; and this fact furnishes another argument 
in favour of the opinion which considers them as distinct. The 
black-toed gull, described by Bewick, appears to have been the 
young of the black species three months old, and the one de- 
scribed by Pennant, bears strong marks of having been the 
young of the white species, but older ; for, as is the case with 
all .the individuals of this genus, a considerable time elapses be- 
