LARlDJi— TUE GULLB AND TEliNS. 219 



Family LARIDJE.— The Gulls and Terns. 



CHAnACTEES. Bill moderately compressed, or sometimes nearly cylindrical, Its cover- 

 ing entire; the tip of the maxilla overhanging, or at least meeting, that of the mandible; 

 the culmen more or less curved, but never arched, terminally— sometimes nearly straight 

 throughout; symphysis of the m :ndiblo usually forming more or less of an angle, this. In 

 most cases, prominent in proportion to the relative depth of the bill; nostrils sub-basal, 

 perforate; legs and feet of proportionate size. Tail extremely variable in form an length. 



Although induding among its very numerous members great 

 extremes of size and form, the family LaridcB as here restricted 

 is not divisible into more than two subfamilies; and these 

 are so nearly united through certain forms as to be really 

 more artificial than natural. They may, with considerable 

 difficulty, be defined as follows: 



Subfamily Larinae. Depth of bill decidedly greater at the angle than at the nostril; 

 terminal portion of culmen decidedly curved; angle at lower mandible always distinct, 

 often very prominent; tail usually even, but sometimes slightly emarglnate (Rissa), 

 deeply emarginate (Xema), forked (Ureagrus) or graduated (RJiodostethia). Size, 

 extremely variable (wing 8.75-20.00). 



Subfamily Sterninse. Depth of bill at angle lees than a' 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 inAnous). 

 Size extremely variable (wing 6.50-17.50). 



The North American genera may be distinguished by the fol- 

 lowing characters: 



Subfamily LARIN-SJ.— The Gulls. 



A. Tarsus roughened or serrate behind. 



1. Gavia. 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. (Not represented in the Illinois fauna.) 



B. Tarsus not roughened or senate behind. 



a*. Hind toe rudimentary or altogether absent. 



2. Bissa. 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 spcciies) also with a black patch. 



a'. Hind toe perfectly developed, though small. 



