240 BIBDB OF ILLINOIB. 



Genus STERIfA Linn^us. 



sterna Ltnn. B. N. ed. 10, i, 1758,137, ed. 12, i, 1766. 227. Type, by elimination. Sterna hirundo 



Linn. 

 Bternula BoiE, Isis, 1822, 563. Type, Sterna minuta Linn. 

 Thalasaeus BoiE, Isis, 1822, 563. Type, Sterna cUspia Pali,. 



Thalassea Kaup, Sk. En*w. Eur. Thierjy. 1829, 97. Type, Sterna paradUcea Bbi^nn. 

 Sylochelidun Bkehm. Tog Deutsohl. 1830, 767. Type, Sterna caspia Ijvstsi. 

 A'ctoohe.Udnn Kaup, Sk. Ent. Eur. Tiiierw. 1829, 31. Type, Ste na cantiaea GuEL. 

 Haliplana Wagl. Jsis, 1832, 1234. Type, Sterna fulignesa Gmel. 



Bp. Chab. BUI much more slender than In Grelochelidon, its depth through the base 

 less than one third the length of the exposed oulmen, its upper outlines never strongly 

 curved and its lower outline always straight, or nearly so. Size exceedingly variable, the 

 form and colors less so ; tail always decidedly forked.and toes almost fully webbed, but the 

 webs concave, or "scalloped out," anteriorly. 



The above diajrnosis covers several groups of species, usually 

 ranked as subgenera, some of which are possibly entitled to full 

 generic rank, since they appear to be quite as distinct from typ- 

 ical Sterna as is Gelochelidon. 



The species occurring in eastern North -America are the fol- 

 lowing : 



A Wing more than 9.00 inches. 



o. Size very large (wing 15.00 inches or more); tail elnarginate; occipital feathers soft and 

 blended, not forming a crest; inner webs of primaries concolored (dusky grayish); 

 adult, above, pale pearl-gray, beneath, white: hood wholly black in summer, wholly 

 streaked or speckled with white in winter, (-iubgenus Thalasseus BoiE.) 



1. S. tsohegr ' va. Bill very robust (the depth through the base a little less than one 



third the lengtji of the oulmen), deep red. 

 6. Size large or medium (wing 12.50-15 inches); tail deeply forked; occipital feathers 

 pointed and somewhat lengthened, forming a short but distinct crest; inner webs 

 of primaries bioolored (dusky in a weli-deflned stripe next the shaft, the inner edge 

 broadly and abruptly white); adult, pale pearl-gray above, white beneath; plleum 

 wholly black in spring, the forehead, lores, and centre of the crown white in the 

 breeding season. (Subgenus /4 ctocfteMoJi Kaup,) 



2. S. maxima. Bill stout (but depth through the base much less than one third the 



length of the culmen), deep orange; wing, 14.00rl5.00 inches. 



3. S, sandvioensis aouflavidus. Bill very slender, deep black, tipped with yellow. 



Wing, about 12.60 inches, 

 c. Size small (wing less than 12.00 but more than 8.00 inches) ; 'tail of adult excessively 

 forked, with lateral feathers very narrow towards tips; occipital feathers soft and 

 blended, not forming a crest. 

 i. Upper parts pearl gray, the whole top of head black In summer; tall white or 



pate pearl-gray. (BubKenus SfernoLiNN.) 

 IT. Only one web of outer tail-feather .entirely white. ' 



4. S. forsteri. Lower parts entirely white; outer web of lateral tall-feather entirely 



white, the inner web usually grayish or dusky near end. 

 8. 8. hirundo. Lower pa,ts pale gray or grayish white; outer web of lateral tall- 

 feather grayish or dusky, the Inner web entirely white. 



