LARIDZ. 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. 
Hab. Northern parts of northern hemisphere, breeding in Arctic regions; 
south, in winter, to California, Florida, ete. 
38. S. longicaudus ViziLt. Long-tailed Jaeger, 
Famity LARIDA®.—Tue Gutis anp 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 (Rhodostethia). 
Size extremely variable (wing 8.75-20.00). (Subfamily Zarine.) 
6°. 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.) 
6%. 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..........c.ccccseeeees Rissa. (Page 24.) 
c’, Hind toe perfectly developed, though small. 
d', Culmen decidedly more than two-thirds as long as tarsus. 
é. Tail even; size, color, and all other characters extremely vari- 
BDC casanzsseotsamabacyapensaseus semdaneoepansenn Larus. (Page 25.) 
é. Tail deeply emarginate or forked............ Kema. (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 PAIL.......ssseceereeeeeeerenees Rhodostethia. (Page 37.) 
a. 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 Sternine.) 
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 Jower parts. 
