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). 



Lams glaucus. Glaucous Gull. 



See Xo. 24. 



Outer webs of primaries, dark brown; wing, over 17.50; depth of bill at angle, over .90 

 (immature). Larus marinus. Great Black-backed Gull. 



See No. 27. 



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

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



See No. 30. 



Section 3. Length, over 21 ; bill, under 2; underparts, white. 



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



Larus argentatus smithsonianus. American Herring Gull. 



See Xo. 30. 



Back, pale pearl color; pri- 

 maries, whitish or pearl color, 

 shading to white at tips. 



Larus leucopterus. 

 Iceland Gull. 

 See Xo. 2o. 



Ring-billed Gull. 



Back, pale pearl color; primaries 

 marked with slaty gray. 



Larus knmlieni. Kumlien's Gull. 

 See No. 26. 



Herring Gull. 



