AVES LARID^I. 225 



yellow, orbital ring white (Saunders). Tarsi: Vermilion. Feet: Toes 

 vermilion, the hallux joined- to the inner toe by a distinct web. 



Young of the year have the head dusky grey, the neck entirely brownish. 

 The mantle is dark brown. The first five primaries are black, 'without 

 white tips, the remainder much as in older birds. The secondaries are 

 almost as broadly tipped with white as in adults. 

 Upper tail coverts white with a faint grey tinge. Tail IG 



white with a broad subterminal black band. The lower 

 parts are white, faintly tinged with grey up to the breast, 

 which is brownish like the neck. The bill is deep yel- 

 low at the base, shading into dusky and becoming 

 almost black anteriorly. The legs and feet are pale 

 brown. 



Older birds of the year are distinguished by a sooty jf. 



head, in contrast to the neck which is grey. The man- Leucophans scores- 



tle is much darker centrally and the band on the tail &- Older bird of the 

 11 ^i L 1-1 year. About X nat ~ 



narrow and absent on the two outer rectnces which . . 



ural size. 



are nearly white. The under surface is pale grey. 



Immature birds have a well defined sooty hood and are otherwise much 

 like adults, though there is less white on the primaries. 



Downy nestlings, cold slate grey closely and finely spotted above with 

 dark umber and mottled below with the same color on a similar ground 

 shade. 



Geographical Range. As given for the genus, this being the sole 

 representative recognized. 



This Gull was not obtained by the Princeton Expeditions to Pata- 

 gonia and the descriptions here given are based on the material in the 

 British Museum of Natural History and also on specimens obtained from 

 the Museo de La Plata. The bird is said to be quite localized in distri- 

 bution even in the regions where it occurs. In habit it is somewhat 

 parasitic and decidedly predatory, feeding on the eggs and young of other 

 Gulls and birds which breed in communities ; and during the non-breed- 

 ing season of the year shell fish of various kinds are largely consumed by 

 these birds which do not subsist to a great degree on fish. 



