220 AVES: LONGIPENNES. — XXXII 
331. RISSA Leach. (Icelandic name.) 
647. R. tridactyla (L.). Kirtiwaxe Gui. Mantle bluish- 
gray ; head, etc., white; hind claw a minute knob, sometimes ab- 
sent. L.16t018. W.12. Arctic, S.in winter toN. Y. (Au) 
(Lat., tres, three ; dactylus, digit.) 
332. LARUS Linneus. (Adpos, gull.) 
u. Head entirely white in adult in summer (young more or less dusky on 
head, etc.); mantle grayish blue, or dusky; lower parts white. (Larus.) 
6. Primaries, without any black, pearly-gray, whitish at tip. 
648. L. glaucus Briinnich. Ick Gutt. BurGomasTeErR. 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. (Hu) 
(yAaukes, bluish.) 
649. L. leucopterus Faber. IceLtanp Gut. Similar but 
smaller. L. 25. W.154. T. 64. B. 13. Same region. (Eu.) 
(Acuxés, white; mrepov, wing.) 
bb. Primaries with white and dusky (sometimes all black in young). 
ce. Dark spaces on primaries gray. 
650. L. kumlieni Brewster. Similar to L. leucopterus. L. 24. 
W.16. B. 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 Biack-Backep Gutu. Mantle 
blackish slate color; largest of our gulls. L. 30. W.18. B. 2h. 
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. 2}. 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. (Eu.) 
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.18. 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. (Chra- 
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. TT. 
5. B.1g. E.U.S., coastwise. (Lat., ater, black; cilla, tail.) 
ee. Tarsus not longer than middle toe and claw. 
