LARID^. 23 



slate-color, more ashy on back ; quills and tail-feathers blackish toward 

 tips ; chest (sometimes breast also), and more rarely the belly, white, 

 shading into grayish, the under tail-coverts, sides, and flanks (usually 

 belly also) uniform slate-gray. Length 20.00-23.00, wing 11.55-12.85 

 (12.25), longest tail-feathers 10.50-14.50 (12.89), culmen 1.10-1.30 (1.19), 

 tarsus 1.50-1.80 (1.66), middle toe 1.08-1.30 (1.20). Eggs 2.16 X 1.54. 

 Hah. Northern parts of northern hemisphere, breeding in Arctic regions; 

 south, in winter, to northern United States. 



38. S. longicaudus Vieill. Long-tailed Jaeger. 



Family LARIDiE. — The Gulls and Terns. (Page 20.) 



Genera. 



a\ Depth of bill decidedly greater at the angle than at the nostril ; terminal por- 

 tion of culmen decidedly curved ; angle of lower mandible always distinct, 

 often very prominent ; tail usually even, but sometimes slightly emarginate 

 (Rissa), deeply emarginate or forked (Xema), or graduated (RJiodostethia). 

 Size extremely variable (wing 8.75-20.00). (Subfamily Larince.) 

 ¥. Tarsus roughened or serrate behind. 



Tail even ; tarsus shorter than middle toe, with claw ; hind toe perfectly 

 developed, but small ; size medium (wing about 13.25) ; color entirely 



white, the young scantily spotted with dusky Gavia. (Page 24.) 



b^. Tarsus not roughened or serrate behind. 



c\ Hind toe rudimentary or altogether absent. 



Tail slightly emarginate; tarsus shorter than middle toe, without 

 claw ; size medium (wing about 12.00-13.00) ; adult white, with 

 bluish gray mantle ;^ young, similar to adult, but hind neck with 

 a blackish patch, and lesser wing-coverts sometimes (in one spe- 

 cies) also with a black patch Rissa. (Page 24.) 



c^ Hind toe perfectly developed, though small. 



d^. Culmen decidedly more than two-thirds as long as tarsus. 



e\ Tail even ; size, color, and all other characters extremely vari- 

 able Larus. (Page 25.) 



e*. Tail deeply emarginate or forked Xema. (Page 37.) 



d^. Culmen decidedly less than two-thirds as long as tarsus. 



Tail graduated, the lateral feathers .75-1.25 shorter than the 



middle pair Rhodostethia. (Page 37.) 



o^ Depth of bill at angle less than at middle of nostrils ; terminal portion of culmen 

 straight, or but slightly curved, the bill being narrow and pointed ; angle of 

 lower mandible seldom prominent ; tail more or less forked (except in Anous). 

 Size extremely variable (wing 6.50-17.50). (Subfamily Sternince.) 



1 This is a special term used, chiefly in descriptions of birds of this family, to designate the back, scapu- 

 lars, and wings, when together colored differently from the head, neck, rump, tail, and lower parts. 



