550 Capt. Sapine’s Memoir on the Birds of Greenland, $c. 
also rayed with black. The young birds when full grown have 
this autumnal appearance with additional differences correctly. 
described in the Fauna Suecica; the bill is black instead of yel-. 
low; at the back of the neck the feathers are tipt black, forming: 
a narrow crescent-shaped patch; the wing coverts are tipt black, 
forming a bar across the wings ; primary quills black, with more 
or less E the inner webs in didiont specimens white: tail tipt for. 
. half an inch with black, except the outer feather on each side, the 
second having only a spot on the inner web. It is worthy of ob- 
servation that the outer tail feathers are somewhat longer than the 
inner ones, giving the tail an appearance of being slightly forked ; 
this is more perceptible in the young birds than in the old ones. . 
The specific name of tridactylus (though given by Linneus to 
the immature bird) appears preferable, as being more appropriate 
than that of Rissa: it is therefore adopted. I am inclined to 
suppose that this species attains maturity at the age of one year. 
In June none were seen with spotted plumage; early in October 
several immature birds were killed, being marked as above de- 
scribed: the specimens noticed by Montagu as killed in the 
month of March, and supposed by him to be i in complete plu- 
mage, had evidently not got rid of all the black markings on the 
wing coverts, which I believe would have taken place, had they 
lived a few weeks longer. 
The L. tridactylus of Gmelin and Müller, and the Tarrock Gull 
of the Arctic Zoology, are the young bird afterit has lost the black 
bar upon the wing, and before the colour has disappeared from 
the neck and from the tips of thetail-feathers. Itis apprehended 
that the Larus cinerarius of Fabricius is the tridactylus in winter 
plumage: its rarity in Greenland, as noticed by him, may be ac- 
counted for by the probability that most of these Gulls migrate 
southwards during that season. 
23. Larus 
