LABIDjE— THE GULLS AND TEBNS. 219 



Family LARID^.— The Gulls and Terns. 



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

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

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

 throughout; symphysis of the m mdible usually forming more or less of an angle, this, in 

 most cases, prominent In proportion to the relativO depth of the blU; nostrils sub-basal, 

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

 diflBculty, be defined as follows: 



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

 terminal portion of oulmen d eidedly curved; angle at lower mandible always distinct, 

 often very prominent; tall usually even, but sometimes slightly emarginate (Bissa), 

 deeply emarginate iXema), forked {Greagrus) or graduated (Bhodostethia). Size, 

 extremely variable (wing 8.75-20.00). 



Subfamily Sterninse, 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; tall more or less forked (except ia. Anous). 

 Size extremely variably (wing 6.50-17.50). 



The North American genera may be distinguished by the fol- 

 lowing characters : 



Subfamily LABIN.S:.— The Gulls. 



Tarsus roughened or serrate behind. 



1. Qavia. Tall 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.) 



Tarsus not roughened or ser, ate behind. 

 . Hind toe rudimentary or altogether absent. ' 



2. Bissa. Tall 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) aMo with a black patch, 



, Hind toe perfectly developed, though smaU. 



