LARID.E— THI-] GULLS AND TERNS. 219 



Family LARID.ZE.— The Gulls and Terns. 



Characters. Bill moderately compressed, or sometimes nearly cylindrical, its • 

 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 mdible 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 Zqridce 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 emarginate (Iiissa), 

 deeply emarginate (Xema), forked {Creagrus) or graduated llthodostethia). Size, 

 extremely variable (wing 8.75-20.00). 



Subfamily Sterninae. 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 J 17.5O). 



The North American genera may be distinguished by the fol- 

 lowing; charnchTs : 



Srr.i amii.v LARIN^ffi.— Tin-: Gulls. 



A. Tarsus roughened or serrate behind. 



1. Gavia. Tail even; tarsus shorter than middle toe with ''law; bind toe perfectly 

 developed, bul small; size medium (wing about 13.25); color entirely white, the 

 younc scantily spotted with dusky. (Nol represented in the Illinois raw 



B. Tarsus no1 roughened or sit, ate behind. 



,i\ Hind ton rudimentary or altogether absent. 



2. Rissa. Tail Bllghtly emarginate; tarsus shorter than middle toe without .'law; 

 size medium (wing about 12.00 18.00) ; adult white, with bluish gray mantle; 

 f/oung, .similar to adult, but. hind neok with a blaoktsb patch, and !■ 



coverts sometimes (in one speoles) also with a blaok patch. 

 --. Hind too perfoctly developed, though small. 



