LARID.E— THE GULLS AND TEllNS. 219 



Family LARID^.— The Gdlls and Terns. 



Chabacteks. Bill moderately compressed, or sometimes nearly cylindrical, its oover- 

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

 the oulmen 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 l length. 



Although inchidiiig amouo; its very numerous members great 

 extremes of size and form, the family Lariche 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 

 diflBculty, be defined as follows: 



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

 terminal portion of culmen d' cidedly curved; angle at lower mandible always distinct, 

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

 deeply emarginate [Xema). forked {Creaoms) or graduated iRhodostethia). Size, 

 extremely variable (wing 8.75-20.00). 



Subfamily Steminse. Depth of bill at angle loss than a^ middle of nostrils; terminal 

 portion of oulmen straight, or but slightly curved, the bill being narrow and pointed: 

 angle of lower mandible seldom prominent; tail more or less forked (except In Anoua). 

 Size extremely variable (wing 6.50-l7..i0). 



The North American genera may be distinguished by the fol- 

 lowing characters: 



Subfamily LARIN-ffi.— The Gullb. 



A. Tarsus roughened or serrate behind. 



1. Oavia. 'I ail pven; 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 lu the Illinois fauna.) 



B. Tarsus not roughened or sor ate behind. 



u'. Hind toe rudimentary or altogether absent. 



2. Bisia. Tall sightly emarginate : tarsus shorter than middle toe without claw; 

 bIzo medium (wing about 12.00-13.(W): adult white, with bluish gray mantle; 

 VounQ, simi'ar tu adult, but hind neok with a blackish patch, and lesser wing- 

 coverts Bomotimes (la one species) also with a black pat«h. 



a*. Hind toe pertecUy developed, though small. 



