576 



BULLETIN" 50, UNITED STATES NATIONAL MUSEUM. 



family), with well-developed, rather large, claw; claws of anterior 

 toes large and strongly curved; bare portion of tibia very short, in- 

 cluding only the extreme lower portion. 



Coloration. — -Adults (at least in summer) entirely immaculate 

 white; young (and whiter adults?) white, sparsely spotted with 

 dusky. 



Range. — •Circumpolar regions, south in winter to British Islands, 

 France, Long Island, Lake Ontario, British Columbia, etc. (Mono- 

 typic.) 



PAGOPHILA ALBA (Gunnerus). 



IVORY GULL. 



Adults in summer (sexes alike). — Entirely immaculate white, the 

 shafts of primaries yellowish ; biU greenish gray or ohvaceous (drying 

 more dusky) basally (as far as anterior end of nostrils), the terminal 

 portion yellow (sometimes tinged with red or orange), the tomia 

 yellowish or horn color; isis dark brown; bare orbital ring brick red 

 or vermilion; legs and feet black. 



Winter plumage. — (Undetermined or undescribed.) 



Young. — Similar to adults, but anterior portion of head grayish 

 brown or brownish gray, primary coverts, primaries, tertials, longer 

 scapulars, and rectrices with a terminal or subterminal spot of dusky, 

 and lesser wmg-co verts with small central spots of the same; bill 

 blackish, clouded vnth pale yellowish. 



Downy young. — ^Entirely pure white, even to the base of the down. 



Adult maZf.— Wing, 318-362 (333.6); tail, 128.5-156.5 (137.4); 

 exposed culmen, 31-36 (34.9); tarsus, 33-38 (35.8); middle toe, 

 29.5-36 (33.7).« 



Adult female.— Wm<^, 300-327 (315.7); tail, 133-137 (135); ex- 



posed culmen, 33-34 (33.3); tarsus, 35-39 (36.3; 

 34.5 (33).'' 



middle toe, 31.5- 



a Five specimens. 



& Three specimens. 



