770 SYSTEMATIC SYNOPSIS.— LONGIPENNES—GAVI^. 



315. HYDROCHELI'DON. (Gr. vhap, hudor, water; xe^'S""") chelidon, a swallow.) Black 

 Teens. BiU a little shorter than head, longer than middle toe and claw; very delicate, slender, 

 acute ; culmen and commissure decidedly declinato-convex, the amount of curvature increasing 

 toward the tip ; outline of rami and gonys both concave, the former most so ; eminentia sym- 

 physis prominent and very acute. Wings exceedingly long, pointed, of same color as back, 

 vrithout distinct markings on either web. Primaries broad and not very tapering, not acute ; 

 tertials very short, rounded, not slender nor flowing, reaching in the folded wing only half-way 

 to tip of longest primary. Tail rather short, contained 2i times in the wing, only moderately 

 emarginate (much as in Gehchelidon), the lateral feathers but little exceeding tne next, not 

 tapering and acuminate ; all the feathers broad and rounded. Feet slender and short ; tarsi 

 much abbreviated, rather less than the middle toe alone. Toes moderately long ; the webs 

 rather narrow and very deeply incised (fig. 51). Size small, general form delicate ; colors 

 ' mostly black, the wings and tail plumbeous. 



Atialysis of Species. 



Wings and tail above like back lari/ormis 806 



Wings whitening along border of forearm ; upper tail-coverts white leucoptera 807 



806. H. larifor'mis. (Lat. lariformis, gull-shaped.) Black Tern. Shokt-tailbd Teen. 

 Adult, in summer : Head and neck all around and under parts to the vent, jet black ; under 

 tail-coverts pure white. On back of neck, and between shoulders, the black lightening into 

 leaden-gray, which extends over all the upper parts to the very tips of the tail-feathers. Ter- 

 tials like back ; secondaries darker, tending to the color of the primaries, which are grayish- 

 black, silvered, with paler margins of inner webs, their shafts white except at tips. Lining of 

 vrings ashy-white, reaching a little over border on to lesser coverts. Bill and claws black, 

 angle of mouth lake red ; feet reddish-brown ; eyes brown. In winter : Very different ; fore- 

 head, sides of head, neck all round, and entire under parts, white ; under wing-coverts only 

 ashy-gray. Upper parts generally as in summer, but paler, many feathers with whitish edges. 

 A grayish -black bar along lesser coverts. On the crown, white varied with grayish or ashy, 

 darker on nape, with bar through eye. While changing, head and imder parts patched vrith 

 white and black. Young : Bill brownish-black, base below flesh-color ; mouth yellow ; feet 

 light brown. Forehead grayish-white, deepening on crown and nape to grayish-brown which 

 reaches down to the back, obscuring the plumbeous ; interscapulars quite brown ; on other 

 upper parts the brown edges the feathers. Lesser wing-coverts grayish-black. A black cres- 

 cent before eye. Under parts pure white, the sides of the breast ashy-brown, the sides of the 

 body and lining of the wings ashy. Quills as in the adults, but the shafts of the primaries 

 brown. Length about 9.25 ; extent 25.00 ; wing 8.25 ; tail 3.75, forked 1.00 ; bill along oul- 

 men 1.10; along gape 1.60; height at base 0.25 ; gonys 0.60. Young smaller, about 8.00; 

 biU 1.00 ; tail shorter and less forked. N. Am. at large, interior and coastwise, abundant. 

 Breeds in large colonies anywhere, in marshes and reedy sloughs, in June. Eggs on debris o2 

 dead reeds, often wet and floating, without any nest ; 2-3, 1.35 X 0.95 average, pointed, yet 

 with considerable bulge of the sides ; ground color brownish-olive, rather pale and clear, 

 thickly marked with spots and splashes of every size from dots to masses, but mostly large 

 and bold, of light brown and blackish-brown, and the usual neutral-tint sheU-markings ; ten- 

 dency to aggregate at or around the larger end. 



807. H. leuco'ptera. (Gv. XevKos, leukos, white; irrepou, pteron, wing.) White- WINGED Black 

 Teen. Adult in summer: Bill black, tinged with red; feet red; claws black. Head and 

 neck all around and under parts pure black, shading on back and scapulars into dark slaty 

 plumbeous ; wings dark silvery-plumbeous, fading to white along border of forearm, the quills 

 silvered-dusky vrith white shafts and dull white area on inner webs of the primaries ; lining of 

 wings sooty blackish, varied with white along the border. Tail and its coverts, above and 



