FAMILY LARID^E. GULLS AND TERNS. 



39 



Section 2. Length, over 21; bill, over 2; underparts, 



not white. 



Outer webs of primaries, ash color (immature) . 



Outer webs of primaries, dark brown; wiug, over 17.50; depth of bill at angle, over .HO 



Lnrnx tjlaucus. Glaucous Gull. 



See No. 24. 



(immature). 



Larus mari ii us. Great Black-backed Gull. 



See No. 27. 



Outer webs of primaries, dark brown; depth of bill at angle, under .90; wiug, under 17.50 

 (immature). Larus argentatus smithsonianus. American Herring Gull. 



See No. 30. 



Section 3. Length, over 2 1 ; bill, under 2 ; underparts, white. 



Back, grayish blue, more or less black on primaries. 



Larus ar<i<>ntntus smithsonianus. American Herring Gull. 



See No. 30. 



Back, pale pearl color ; pri- 

 maries, whitish or pearl color, 

 shading to white at tips. 



Larus leur.npti'rus. 

 Iceland Gull. 

 See No. 25. 



Great Black backed Gull. 



Ring-billed Gull. 



Back, pale pearl color; primaries 

 marked with slaty gray. 



Larus kumlieni. Kumlien's Gull. 



See No. 26. 



Herri ii}? Gull. 



