40 



KEY TO THE BIRDS OF EASTERN NORTH AMERICA. 



Section 4. Length, over 21 ; bill, under 2; underparts, 



not white. 



Outer webs of primaries, dark brown; bill, over 1.90 (immature). 



Larus argentatus smithsonianus. American Herring Gull. 



See No. 30. 



Outer webs of primaries, brownish; bill, under 1.90 (immature). 



Larus kumlieni. Kumlien's Gull, 

 See No. 26. 



Outer webs of primaries, ash color (immature), 



Larus leucopterus. Iceland Gull, 



See No. 25. 



Section 5. Length, under 21. 



A baud of black on the bill (adult). Bill, dull yellow, tipped with black (immature). 



Larus delawarensis. Ringbilled Gull. 

 See No. 31. 



Terns. Gulls. 



* Group 5. Wing, over 17 inches long. 



Primaries, marked with more or less black. Larus marinus. Great Black=backed Gull. 



See No. 27. 



Larus glaucus. Glaucous Gull. 



See No. 24. 



No black on primaries. 



* For directions for measurement, see page 9. 



