220 AVES: LONGIPENNES. XXXII. 



331. RISS A Leach. (Icelandic name.) 



647. R. tridactyfa (L.). KITTIWAKE GULL. Mantle bluish- 

 gray ; head, etc., white; hind claw a minute knob, sometimes ab- 

 sent. L. 16 to 18. W. 12. Arctic, S. in winter to N. Y. (Eu.) 

 (Lat., tres, three ; dactylus, digit.) 



332. LARUS Linnseus. (Aapos, gull.) 



a. Head entirety white in adult in summer (young more or less dusky on 

 head, etc.); mantle grayish blue, or dusky ; lower parts white. (JLarus.) 

 b. Primaries, without any black, pearly-gray, whitish at tip. 



648. L. glaucus Briinnich. ICE GULL. BURGOMASTER. Bill 

 yellow with red spot on lower mandible; large. L. 30. W. 18. 

 T. 8. B. 2. Arctic regions; S. in winter to N. Y. (Eu.) 

 (yXavKos, bluish.) 



649. L. leucopterus Faber. ICELAND GULL. Similar but 

 smaller. L. 25. W. 15J. T. 6J. B. If. Same region. (Eu.) 

 (AeuKoy, white; nrcpov, wing.) 



bb. Primaries with white and dusky (sometimes all black in young), 

 c. Dark spaces on primaries gray. 



650. L. kumlieni Brewster. Similar to L. leucopterus. L. 24. 

 W. 16. B. If. Greenland to N. Y. (To Ludwig Kumlien.) 



cc. Dark spaces on primaries black. 

 d. Shafts of primaries white throughout. 



651. L. marinus L. GREAT BLACK-BACKED GULL. Mantle 

 blackish slate color; largest of our gulls. L. 30. W. 18. B. 2. 

 Feet flesh-colored. N. Atl., S. in winter to N. Y. (Eu.) 



dd. Shafts of primaries black in the black markings. 



652. L. argentatus Briinnich. HERRING GULL. COMMON GULL. 

 Mantle pearly-gray ; bill plain. L. 25. W. 1 7. B. 2J. Feet flesh- 

 colored. Northern regions, abundant on all bodies of water. The 

 American form (var. smithsonianus Coues) has the white of outer 

 quill separated from the rest by a band of black. (Jw.) 



653. L. delawarensis Ord. RING-BILLED GULL. Mantle 

 pearly-gray; feet yellowish; bill yellowish, a black band at the 

 tip in adult ; smaller. L. 20. W. 15. B. If. K Am., abundant, 

 S. to Mex. 



aa. Head black or dusky in adult in summer (more or less pale in young); 

 mantle gray; lower parts, etc., white, rosy in breeding season. (Chroe- 

 cocephalus Eyton. ) 

 e. Tarsus much longer than middle toe and claw. 



654. Ii. atricilla (L.). BLACK-HEADED OR LAUGHING GULL. 

 Bill and feet dusky; reddish in summer. L. 15 to 17. W. 13. T. 

 5. B. If. E. U. S., coastwise. (Lat,, ater, black; cilia, tail.) 



ee. Tarsus not longer than middle toe and claw. 



