BIRDS OF NORTH AND MIDDLE AMERICA. 719 



dusky postocular stripe. Young similar to winter adults, but with- 

 out white on sides of occiput, white of foreneck faintly mottled with 

 dusky, and bill smaller. 



Range. — Circumpolar regions, migrating southward in winter. 

 (Three — possible only two — species.) 



KEY TO THE SPECIES AND SUBSPECIES OF URIA. 



a. Depth of bill at gonydeal angle equal to less than one-third the length of exposed 

 culmen; basal portion of maxillary tomium always black, like rest of maxilla; 

 pileum and hindneck deep olive-brown to deep brownish drab; summer adults 

 with sides of head and neck, chin, throat, and foreneck, olive-brown to brownish 

 drab. 

 h. A white orbital ring, continued backward and downward in a narrow post-ocular- 



eupra-auricular streak. (North Atlantic.) Uria ringvia (p. 719).. 



hh. No white orbital ring nor postocular streak. ( Uria troille.) 

 c. Wing averaging shorter (197 in male, 190.7 in female), middle toe shorter (43.9 

 in male, 43.7 in female), and bill averaging less deep at gonydeal angle (13.6 

 in male, 12.9 in female). (Coasts and islands of northern Atlantic Ocean.) 



Uria troille troille (p. 721). 



cc. Wing averaging longer (203.9 in male, 204 in female), middle toe longer (45.9 



in male, 45 in female) and bill deeper at gonydeal angle (14.1 in male, 15 



in female). (Coasts and islands of northern Pacific Ocean and Bering Sea, 



south to California.) Uria troille califomica (p. 724). 



aa. Depth of bill at gonydeal angle more than one-third the length of exposed culmen; 



basal portion of maxillary tomium whitish in adults; pileum and hindneck 



sooty slate-blackish; summer adults with sides of head and neck, chin, throat, 



and foreneck darker olive-brown or clove brown, ( Uria lomvia.) 



b. Averaging slightly smaller (wing 208.2 in male, 203.5 in female; tarsus 35.3 in 



male, 34.1 in female; middle toe 43.6 in male, 44.2 in female); basal portion 



of maxillary tomium more conspicuously whitish. (Coasts and islands of 



northern Atlantic and adjacent portions of Artie Ocean.) 



Uria lomvia lomvia (p. 726). 

 bb. Averaging larger (wing 221.7 in male, 217.2 in female; tarsus 36.7 in male, 36.5 

 in female; middle toe 45.9); basal portion of maxillary tomium less conspicu- 

 ously whitish. (Coasts and islands of northern Pacific Ocean, Bering Sea, and 

 adjacent parts of Arctic Ocean.) Uria lomvia arra (p. 730).^ 



URIA RINGVIA Brunnich. 



RINGED MTJRRE. 



Similar to U. troille, but with a narrow white ring completely 

 encircling eye and continued backward and downward, as a narrow 

 streak bordering upper and posterior margins of the auricular region^ 

 to sides of nape. 



Adults in breeding season (sexes alike). — Head and neck, all round, 

 plain soft grayish brown (between olive-brown and clove brown), 

 relieved by a narrow orbital ring and postocular streak of white, the 

 latter confluent with the former and occupying the crease wliich 

 follows the upper margin of the auricular region; upper parts dusky 

 grayish brown (nearly chsetura drab but more grayish, especially on 

 tips of feathers) , the secondaries narrowly but sharply tipped white : 



