220 



BIRD-i OF ILLINOIS. 



h'. Culmen decidedly more than two third<? as long as tarsus. 



c'. Tail even; size, color, and all other characters extremely variable. 

 S. Laius. 



C-. Tail emarginate or forked. 

 i. Xema. Tail much less than halt as long as wing, and forked for not more than 

 one eighth its length. 



5. Creagrus. Tail nearly half as long as wing, and forked for about one third its 

 length. (JJot represented in the Illinois fauna.) 



b'. Culmen decidedly less than two thirds as long as tarsus. 



6. Bhodostethia. Tail graduated, the lateral feathers .75-1.25 shorter than the middle 



pair. (Not represented in the'Illinois fauna.) 



Subfamily STERNINiE.— The Terns. 



A. Tail more or less forked. I he outer feather longest. 



o. Tail much more than one third a; long as wing, usually (except in subgenus 

 Thalasseus) forked for more than one fifth its total length, the outer feathers 

 narrow and pointed at tips: webs of feet occupying more than half the interdigital 

 space. 



7. Gelochelidon. Depth of bill at base equal to r ne third the length of the exposed 

 culinen; gonys shorter than inner toe, without claw. 



8. Sterna. Depth of bill at base less than one third the length of the exposed cul- 

 men; gonys longer than inner toe, without claw. 



b. Tail httle niore than one third as long as wing, forked for less than one fifth 

 its total length, the outer feathers broad and rounded at tip; webs of feet oc- 

 cupying less than half the interdigital space. 



9. Hydrochelidon. 



B. Tail graduated. 



10. Anous. (Not represented in the Illinois fauna.) 



Subfamily LARIN-ffi.— The Gulls, 



Genus RISSA Leach, 



liissa Leach, Stephens's Gen, Zool. xiii. 1825. 180. Type, l.arus rissa BBiJNN.=i. tri- 

 dactylus Linn. 



Gen. Char. Size medium; tail even, or slightly emarginate; hind toe rudimentary 

 or entirely absent, the nail usually obsolete; tarsus much shorter than the middle toe 

 without its claw, not rough or serrate behind. Adults with head, neck, rump, upper 

 tail-coverts, tail, tips of secondaries, and entire lower parts pure white; mantle bluish 

 gray, the quills varied wiih white and black; bill yellowish, feet blacki>h or bright red 

 in life. Yoiina similar to adults, but hind-neck crossed by a blackish colar or patch, 

 and sometimes in li. tridnctula) a blackish patch on lesser wing-c. verts and black band 

 a.TOss tip of tail Dowtiu young while, tinged above with buffy and yellowish g ay, 

 but without spots or other distin -t marking.-*. Eggs 2—5. ovate, or short-ovate, oliva- 

 ceous white, grayish white, brownish whit'', or buffy, blotehed and spotted with brown 

 and lavender- gray. 



