220 AVES: LONGIPENNES. — XXXII. 
331. RISSA Leach. (Icelandic name.) 
647. R. tridactyla (L.). Kirriwake Guu. Mantle bluish- 
gray ; head, etc., white; hind claw a minute knob, sometimes ab- 
sent. L.16to18. W.12. Arctic, S.in winterto N.Y. (£4) 
(Lat., tres, three ; dactylus, digit.) 
332. LARUS Linneus. (Adpos, gull.) 
a. Head entirely white in adult in summer (young more or less dusky on 
head, etc.); mantle grayish blue, or dusky; lower parts white. (Larus.) 
b. Primaries, without any black, pearly-gray, whitish at tip. 
648. L. glaucus Briinnich. Ick Gutyt. BurGomaster. Bill 
yellow with red spot on lower mandible; large. L. 30. W. 18. 
T. 8 B. 24. Arctic regions; S. in winter to N. Y. (£u.) 
(yAavkos, bluish.) 
649. L. leucopterus Faber. IJIcELAND Gutu. Similar but 
smaller. L. 25. W.154. T. 64. B. 12. Same region. (£uw.) 
(Aevkos, white; mrepdv, wing.) 
bb. Primaries with white and dusky (sometimes all black in young). 
c. Dark spaces on primaries gray. 
650. L. kumlieni Brewster. Similar to Z. leucopterus. lL. 24. 
W. 16, 3B. 1%. 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. 23. 
Feet flesh-colored. N. Atl, S.in winter to N. Y. (£u.) 
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.17. B. 21. 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. (uw.) 
653. L. delawarensis Ord. RiING-BILLED GuLL. Mantle 
pearly-gray ; feet yellowish; bill yellowish, a black band at the 
tip in adult; smaller. L. 20. W.15. B.13. N. 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. (Chre- 
cocephalus Eyton.) 
e. Tarsus much longer than middle toe and claw. 
654. L. atricilla (L.). BLACK-HEADED OR LAUGHING GULL. 
Bill and feet dusky; reddish in summer. L. 15to17. W.13. T. 
5. B.1%. E.U.S., coastwise. (Lat., ater, black; cilla, tail.) 
ee. Tarsus not longer than middle toe and claw. 
