38 KEY TO THE BIRDS OF EASTERN NORTH AMERICA. 



Underparts, white; first primary, entirely black or dark brown (adult). 



Larus atricilla. Laughing Gull. 



See No. 33. 



General plumage, white; back, white; first primary entirely white, or with a blackish 

 spot at tip; hind toe, with nail; bill, yellow. Pagophiln alba. Ivory QuII. 



See No. 22. 



Back, pearl gray ; inner web of primary, white, broadly tipped with black ; a small rudi- 

 mentary hind toe without nail. Jiissa tridactiile. Kittiwake QuII. 



See No. 23. 



* Group 3. Wing, 13 to 15 inches long. 



Uudorparts, white; first primary entirely black, or dark brown. 



Larus atricilla. Laughing QuII. 

 See No. 33. 



General plumage, white; first primary, entirelj' white, or with a dusky spot near tip; hind 

 toe, with nail; bill, less than 1.50; wing, less than 14 ; ])iil, yellow. 



Pagophiln alba. Ivory QuII. 

 See No. 22. 



Underparts, white; inner web of primary, white, broadly tipped with black; a small 

 rudimentary hind toe, without nail. Larus triilactyla. Kittiwake QuII. 



See No. 23. 



Underparts, white ; terminal portion of first primary, black, witii white spot near tip. 



Larus delawarensis. Ring=billed QuII. 



See No. 31. 



Primaries, pale pearl gray, becoming white at tip; bill, over 1.50; wing, over 14. 



Larus leuco][>terus. Iceland QuII. 



See No. 25. 



* Group 4. Wing, 15 to 17 inches long. 

 Section 1. Length, over 21 ; bill, over 2 ; underparts, white. 



No black on primaries (adult "i. Larus (jlaiicus. Qlaucous QuII. 



See No. 24. 



Back, slaty black; primaries, black with more or less white (adult). 



Larus marinus. Qreat Black^backed QuII. 



See No. 27. 



Back, pale bluish, gray, or pearl gray ; primaries, dull black or brownish black, more 

 or less marked with white. 



Larus argentatus smithsonianus. American Herring QuII. 



See No. 30. 



* For directions for measurement, see page 9. 



