600 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 
LARUS THAYERI Brooks. 
THAYER’S GULL. 
“ About the size of LZ. kumlient Brewster, but differing in color of 
mantle, primaries, and having a larger and more heavy bill. 
“The color of the mantle is intermediate between kumlient 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.—Type, 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 in 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, pl., 15.) 
