AVES LARID^E. 2 1 9 



the upper and lower tail coverts are barred with dull brown. The rec- 

 trices are dull brown with greyish brown tips. The bill is dark horn- 

 color, lighter at the tip. The legs and feet are brown and the webs 

 pinkish brown. 



These birds probably do not attain the first adult plumage until the 

 fifth year, and the dark mantle first becomes indicated by some decided 

 black spots or areas on the back. Gradually this color extends till the 

 wings show it. Meantime the upper tail coverts become white and the 

 bill paler yellow. In the next change the primaries have white tips. 

 Later the subterminal mirrors begin to show, and with the first complete 

 adult appe'arance, subapical mirrors are developed, as already described. 

 Finally the old birds, beyond the seventh year probably, show the apical 

 white end to the first primary. 



Downy nestlings are dull stone-color with a faint buffish shading, and 

 scattered brownish black spots about the head and duller mottling of a 

 like character on the back. The under parts are greyish white and the 

 feet and toes dull lead color. 



Geographical Range. South America from latitude 10 south to the 

 Antarctic regions. The Falkland Islands, the South Georgia Islands, 

 South Africa, both coasts, the Crozets and Kerguelen Islands, New Zea- 

 land and lands to the south. 



The Black-backed Gull of the South Atlantic and regions cited is of 

 common occurrence on the coast and in some parts of the interior of 

 Patagonia. In appearance it closely resembles the Great Black-backed 

 Gull, L. marinus, of the North Atlantic, but is very appreciably smaller. 

 Difference in size should serve to distinguish the two in all phases of 

 plumage, and the decorations of white on the two first primaries of adults 

 of L. marinus are always much larger relatively than the same markings 

 are in L. dominicanus. 



The several specimens of L. dominicanus obtained by the Princeton 

 Expeditions to Patagonia, and the material in the British Museum of 

 Natural History have formed a basis for the description given. 



A specimen of this species was collected by J. Koslowsky at Valle del 

 Lago Blanco del Chubut, on September 18, 1899. It is a fully adult bird 

 in breeding plumage. 



