756 SYSTEMATIC SYNOPSIS.— LONGIPENNES— GAVI^. 



Webs incised (©roup STBRNEiE). 



Webs moderately incised. Tail well-formed, generally more than half as long as the wing. Under 

 parts white or light. 



Upper parts pearl-gray. Cap in summer black, or a black bat through eye. 



Bill short and very stout, somewhat gull-like, black. Tarsi much longer than the toes, 



black. Tail lightly forked. Medium size Gelochelidon 



Bill long, large, bright colored, or with yellow tip. An occipital crest. Feet black. 



Forking of tail variable. Of large size Thalasseus 



Bill moderate, slender, usually bright colored, like the feet. No crest. Tail long, deeply 



forked. Size medium and small Sterna 314 



Upper parts dusky. Cap like the back. 



Bill and feet black. A white frontal crescent .... Ealiplana 



Webs deeply incised (feet little more than semipalmate). Tail merely emarginate, hardly or not half 



as long as the wing. Under parts in summer black Hydrochelidon 315 



Nostrils nearly median. No frontal antise, the feathers extending further on culmen than at the sides. 

 Tail double-rounded. Tars! very short. Toes lengthened, the lateral nearly as long as the middle, with 

 full webs. (Group AsoEM. ) 

 Color fuliginous Anoiis 316 



314. STEB'NA. (Latinized from English stern or tern.) Teens. Form typical of the sub- 

 family. Nostrils snb-basal. Frontal antise prominent. Tail more or less forked. Tarsus 

 not shorter than middle toe ■withoiit claw. Lateral toes mnoh shorter than middle. Webs 

 moderately incised. Under parts of adult white, or li^e back. (Characters of the subfamily, 

 exclusive of Hydrochelidon and Anoiis.) 



Analysis qf Subgenera arid Species {adults). 



Gi:lochelidon. Bill very stout, almost gull-like, black. Tarsus much longer than toes, black. Tail 

 lightly forked, contained about 2^ times in wing. Size moderate. 



Head crested. Cap black. Pearly mantle extending over rump and tail anglica 792 



Thalasseus. Bill long, large, tern-like, bright colored or with yellow tip. Feet black. Head crested. 

 Size large to largest. 

 Tail merely emarginate, contained nearly or about 3 times in wing. Primaries without white space 



on inner webs, Bill red. Largest: wing about 16.00; tail 5.50; bill nearly 3.00 caspia 793 



Tail forked. Primaries with white space on inner webs. Bill orange, stout, about 2.50, 0.50 or more 



deep at base; gonys about 1.00 long. Wing 14.60 ... maxima 794 



Tail forked. Primaries with white space on inner webs: Bill orange, slender, about 2.50, tinder 0.60 



deepat base, gonys about 1.50 long. Wing 12.50 . elegans 795 



Tail deeply forked, with narrow outer feathers. Primaries with white space on inner webs. BUI 



Blender, black, yellow-tipped ... . caniiaca 796 



Sterna proper. Bill long, slender, acute. Tarsus not longer than middle toe and claw. Tail more or 

 less forked, with acute or very narrow lateral feathers, one-half or more as long as wing. Head not 

 decidedly crested. Size medium to smallest. 

 Mantle pearly-blue. 

 No black cap. 



Head whitish, with black bar through eye ; under parts like the mantle trudeaui 802 



A black cap. 



No white-frontal crescent ; black cap reaching bill. 

 Bill wholly or mostly red or reddish. 



Bill red, blackening at end ; feet coral-red. Outer web of outer tail-feather white ; 



inner gray or dark. Tarsus 0.90 or more .... /orsteri 798 



Bill red, blackening at end ; feet coral-red. Outer web of outer tail-feather gray or 



dark, inner white ; under parts paler than upper. Tarsus about 0.75 . . hirundo 797 

 Bill wholly red; feet vermilion ; outer tail-feather as in the last. Tarsus 0.65 or less. 



Under parts nearly like upper . . . . macrura 799 



Bill black, or only red at base. Feet reddish . . dougalli 800 



A white frontal crescent. 



Bill yellow, tipped with black. Feet yellow aaitillarum 801 



Bill and feet black aleutica 803 



Mantle dusky. A white frontal crescent. Bill and feet black. (Haliplaua.) 



Mantle blackish-brown ; cap the same fuliginosa 804 



Mantle sooty-gray; cap black aruBsthetica 806 



Obs. Above analysis based on adult summer birds, and not entirely available for young and winter ones, 

 In which the chars, of the cap, and colors of bill and feet, may be entirely different. These must be de- 

 termined by reference to the detailed descriptions. 



