1004 



S YS TEMA TIC SYNOPSIS. — L ONGIPENNES. 



Bill orange, stout. Wing 14.50 ; tail 7.00 ; bill 2.50, its depth at base 0.50 or more ; gonys 1.00 . . maxima 

 Bill orange, slender. Wing 12.50 ; tail 7.50 ; bill 2.50, its depth at base under 0.50 ; gonys 1.50 . . elegans 



Bill black tipped with yellow. Wing 12.50 ; tail 0.00 ; bill 2.25 sandvicensis acuflavida 



Of medium to smallest size ; wing 12 00 or less ; bill under 2.00. Head not crested. 

 Mantle pearly. Wing over 8.00. (Sterna proper.) 

 No black cap. 



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



A black cap 



No white frontal crescent ; black cap reaching bill. Feet not black. 

 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. Under parts white. Tarsus 0.90 or more Jorsteri 



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 



Bill wholly red ; feet vermilion. Outer tail-feather as in the last. Under parts nearly like up- 

 per. Tarsus 0.C5 or less paradiscea 



Bill black, or only red at base ; feet red. Both webs of outer tail-feather white. Under parts 



white. Tarsus 0.85 . dovgalli 



A white frontal crescent Bill and feet black aleutica 



Mantle pearly. Wing under 8.00. (Stehnuia.) 



A white frontal crescent. Bill and feet yellow, former black-tipped antillarum 



Mantle dusky. Wing over 8 00. A white frontal crescent. Bill and feet black. (Onychoprion.) 



Mantle blackish-brown ; cap the same fuliginosa 



Mantle sooty-gray ; cap black ancestheia 



Obs. — Above analysis based on adult svimmer birds, and not entirely available for young and winter ones, in which 

 the characters of the cap, and colors of bill and feet, may be entirely different. These must be determined by reference 

 to the detailed descriptions. 



(Subgenus Thalasseus.) 



S. (T.) cas'pia. (Of the Caspian Sea. Fig. 690.) Caspian Tern. Imperial Tern. Of 

 inaxiinuin size. Length 20.00-23.00; extent 50.00-55.00; wing 15.00-17.00, usually about 

 16.00; tail only 5.00-6.00, forked about 1.50, middle feathers broad to their rounded ends, rest 

 growing successively more acute, but lateral pair ivithout any slender filamentous development. 





Fig. O'JO. — Caspian Tern, | nat. size. (From Brehm.) 



Bill extremely large, 2.75 along culmen, 4.00 along gape, 0.90 deep at base, 0.50 wide at 

 nostrils; culmen regularly curved from base to tip; outline of mandibular rami slightly con- 

 cave ; gonys about straight ; angle not very well marked. Tibiae bare about 0.75 ; tarsus 1 .75, 

 rather exceeding middle toe and claw, the scutella in front replaced by polygonal scales similar 



