LARID.T.. 23 



slate-color, more at-lij" on back ; quills and tail-foathcrs blackish toward 

 tijts ; chest (sometimes breast also), and more rarely the boJh-, -white, 

 shading into graj'ish, the under tail-coverts, sides, and flanks (usuallj- 

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

 (12.25), longest tail-toathers 10.50-U 50 (12.89), culmen 1.10-1.30 (1.19), 

 tarsus 1.50-1.80 (1.60), middle toe l.OS-1.30 (1.20). Eijgs 2.16 X 1-54. 

 Ilab. Northern parts of northern hemisphcro, breeding in Arctic regions; 

 south, in winter, to California. P'lorida, etc. 



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



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



Genera. 



aK 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 slighth" emarginate 

 {Rissa), deeplj- emarginate or forked (A'e/nrt), or graduated (Rhodostethia). 

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

 V-. Tarsus roughened or serrate behind. 



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

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



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



6'. Tarsus not roughened or serrate behind. 



&. 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. 



rf'. 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 deeplj- 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.) 



a'. Depth of bill at angle loss than at middle of nostrils; terminal )iorlion 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 Stei'nina;.) 



' This 18 .1 special term used, chiefly in descriptions of birds of this family, to designate the back, scapu- 

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



