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 kumlient. Kumlien’s Gull. 
See No. 26. 
Outer webs of primaries, ash color (immature). Larus leucopterus. Yceland Gull, 
See No. 25. 
Section 5. Length, under 21. 
A band of black on the bill (adult). Bill, dull yellow, tipped with black (immature). 
Larus delawarensis. Ring-billed Gull. 
See No. 81. 
Terns. Gulls. 
ae 
7 
“Group 5. Wing, over 17 inches long. 
Primaries, marked with more or less black. Larus marinus. Great Black=backed Gull. 
See No. 27. 
No black on primaries. Larus glaucus. Glaucous Gull. 
See No. 24. 
* For directions for measurement, see page 9. 
