38 KEY TO THE BIRDS OF EASTERN NORTH AMERICA. 



Underptirts, wlute; first primary, eutirely black or dark l)r<)wn (adult). 



Lams atricilla. Laughing QuII. 

 See No. 33. 



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

 spotatti]); hind toe, with nail; bill, yellow. Pagophila alba. Ivory Gull, 



See No. 22. 



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

 mentary hind toe without nail. Jiissa tridactijle. Kittiwake Gull. 



See No. 23. 



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



TJud.'rparts, white; first primary eutirely black, or dark lirown. 



Lnrus atricilla. Laughing Gull. 



See No. 33. 



General plumage, white ; first primary, eutirely white, or with a dusky spot near tip ; hiud 

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



Pagophila alha. Ivory Gull. 

 See No. 22. 



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

 rudimentary hind toe, without nail. Lams tridaclyla. Kittiwake Gull. 



See No. 23. 



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



Larus dclawaronsis. Ring^billed Gull. 



See No. 31. 



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



Larus leucopterus. Iceland Gull. 

 See No. 25. 



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

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



No blackon primari<'.s (iidult^. Larus tjlaucus. Glaucous Gull. 



See No. 24. 



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



Larus marinus. Great Black^backed Gull. 



See No. 27. 



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



or less marked with white. 



Larus uryentatus smithsonianus. American Herring Gull. 



See No. 30. 



* For directions for me;isuremciit, see page <). 



