LAR1D.E THE GULLS AND TERNS. 219 



FAMILY LARID2E. THE GULLS AND TERNS. 



CHABACTEBS. 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 .ndible 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 i length. 



Although including among its very numerous members great 

 extremes of size and form, the family LaridoB 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 

 dimculty, be defined as follows: 



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

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

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

 deeply emarginate (Xema), forked (Creagrus) or graduated (Rhodostethia). Siae, 

 extremely variable (wing 8. 75-20.00). 



Subfamily Steminae. 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-ffi. 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 1 . Hind toe rudimentary or altogether absent. 



2. Rissa. 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 species) also with a black patch. 



a*. Hind toe perfectly developed, though small. 



