600 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 



LARUS THAYERI Brooks.^ 



THAYER'S GULL. 



''About the size of L. Icumliem Brewster, but differing in color of 

 mantle, primaries, and having a larger and more heavy bill. 



"The color of the mantle is intermediate between Jcumlieni and 

 argentatus, darker than the former, lighter than the latter. 



"The first primary is broadly tipped with white, the outer web 

 blackish slate (Ridgway's Nomenclature of Color), on the inner web 

 this color extends rather less than one-half across the web; second 

 primary similar only with subterminal black band and blackish 

 slate on inner web more narrow, on the outer web it does not extend 

 so near the base of the feather as on the first; third primary with 

 white tip, blackish slate on outer web less extensive, on inner web 

 the black is limited to a subterminal patch about 35 mm, long ex- 

 tending across web; fourth primary with white tip, blackish slate on 

 outer web extending about 45 mm., on inner web about 20 mm., 

 fifth primary with white tip, then subterminal blackish slate band, 

 then narrow poorly defined bar of white. 



" Measurements.— Tji)e, adult male: Wing, 406; tail, 167; tarsus, 

 65; bill, 57. 



"Description of immature male taken by Joseph Dixon at Griffin 

 Point, Arctic Alaska, June 25, 1914. Orig. No. 3752: First primary 

 fuscous hair-brown on outer web, lighter on inner web, changing to a 

 neutral gray, with narrow whitish tip; second primary similar but 

 slightly darker on inner web, especially near tip where it is as dark as 

 outer web, and extends to outer edge; third primary the same; 

 fourth primary similar except that outer web has narrow lighter edge, 

 and inner web for the most part neutral gray; fifth primary similar 

 but no brown on inner web except a patch near the tip which extends 

 across the web. 



"The tail feathers are white with subterminal patches of fuscous 

 hair-brown varying in size, being smaller on the outer feathers. 



" The inner secondaries have light brown areas on outer webs 

 about 30 mm. long, with pallid neutral gray edges." (Original 

 description.) 



Breeding in the high Arctic islands of northern Canada from Elles- 

 mere Land westward to Banks Island, migrating south m winter 

 chiefly on the Pacific coast to Vancouver Island, British Columbia; 

 only one record from the Atlantic coast (Tadousac, Quebec, July 26). 



« Since the manuscript of this article was written, the material on which this sup- 

 posed species was based, together with additional specimens, has been examined by 

 Dr. Jonathan Dwight, Jr., who has found that complete intergradation with L. argen- 

 tatus is clearly shown. Therefore, according to Dr. Dwight, the form should be 

 known as Larus argentatus thayeri. (See Auk, xxxiv, Oct., 1917, 413, 414, pi., 15.) 



