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. 
b. A white orbital ring, continued backward and downward in a narrow post-ocular- 
supra-auricular streak. (North Atlantic.)............... Uria ringvia (p. 719). 
bb. 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.) ............2---.2-2-- Uria troille californica (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 Artic 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 Briinnich. 
RINGED MURRE. 
Similar to U. éroille, 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 which 
follows the upper margin of the auricular region; upper parts dusky 
grayish brown (nearly chetura drab but more grayish, especially on 
tips of feathers), the secondaries narrowly but sharply tipped white: 
