LARUS. 29 
Jf? Two outer primaries with a distinct gray wedge on inner web. 
g. Depth of bill through angle contained less than four 
and a half times in the length of the tarsus; lower 
mandible with a red subterminal spot. 
i, Mantle deep plumbeous-gray, inclining to slate- 
color. 
#, Culmen 2.22 or more; depth of bill at angle 
75 or more; third quill with a distinct 
white “mirror” or large spot on inner 
web between the black and the gray ; 
mantle nearly the same color as in L. 
occidentalis, but averaging alittle darker ; 
rest of plumage (except primaries) pure 
white; feet dull purplish flesh-color in 
life ; length about 26.50, wing 16.75-19.00, 
culmen 2.15-2.35, depth of bill through 
angle .75-.90, at base .75-.82, tarsus 2.60- 
2.75, middle toe (without claw) 2.08-2.40. 
Hab. Coast of ‘northeastern Asia, from 
Japan (?) to Kamtschatka and north- 
ward to Arctic Ocean north of Bering’s 
Siraltivuscesees 48. L. schistisagus Srzsn. 
Slaty-backed Gull. 
#. Culmen 2.15 or less; depth of bill at angle not 
more than .65; third quill without white 
spot on inner web between black and gray ; 
mantle same color as in F. occidentalis, 
but apparently averaging a little paler; 
rest of plumage (except primaries) pure 
white; feet yellow in life; length about 
20.00, wing 16.50-17.25, culmen 2.00-2.15, 
depth of bill at angle .62-.65, at base .65- 
.70, tarsus 2.60-2.72, middle toe 1.78-2.10.! 
Hab. Northern Asia; accidental in south- 
ern Greenland. 
50. L. affinis Rein. Siberian Gull. 
i, Manile light plumbeous-gray, or lighter. 
@, Bill without black spots in adult. 
j. Mantle plumbeous-gray, or very deep 
pearl-gray ; eyelids (in life) orange- 
red, and feet yellow; otherwise ex- 
actly like argentatus and smithso- 
nianus, with the markings of the 
1 The specimens measured are all females. 
Males would somewhat exceed these dimensions. 
