L ARID jE — STERN IN M : TERNS. 765 



a moderate distance; tarsi exceedingly sliort, being less than middle toe without claw, or 

 only equal to it ; toes rather long for the size of the feet ; the outer falls but little short of 

 the middle mic, while the tip of the claw of the inner hardly reaches beyond the third articula- 

 tion of the middle one. The feet are a lighter tint of the color of bill, tending toward vermilion, 

 or coral-red, but not so light as those of hirundo. Wings very long; primaries narrow, 

 tapering to their roundish but slender tips ; shafts white, with scarcely darker tips. Outer 

 web of first primary grayish-black, hghtening into silvery-gray at tip ; inner web white, 

 with only a very narrow line of grayish-dusky along the shaft; this dusky space much 

 narrower and lighter than in hirundo ; next four or five primaries sUvery-gray, darkest 

 toward their tips ; their inner webs mostly white (wholly so at their bases) ; but the white 

 does not extend so far toward the tips of the feathers as on the first primary, and it runs up 

 fartlier in the centre of the web than on the edge of it. Inner primaries of the color of 

 the back, broadly tipped and margined internally with white. Tail exceedingly long, the 

 exterior fe;fther being as much lengthened, and as narrow, tapering and acute, as in S. dougcdli. 

 The tail-feathers reach beyond the tips of the folded wings. Tail pure white, the outer web 

 of its exterior feather being grayish-black, ligliter basaUy, and its inner web, and the outer 

 webs of tlie next two reotrices, having a consideraUe wash of pearl-blue. Cap pure, lustrous 

 greenisli-black, so broad on the cheeks as to leave only a slender line of white to extend along 

 the edge of the feathers on the side of the upper mandible. Upper parts pearl-blue, of about 

 the same shade as in hirundo ; this color, however, fading into white at tips of tertials and 

 inner secondaries. Under parts but a little lighter shade of the color of the back, fading 

 insensibly into whitish on the chin, throat, and edges of the black cap, and ending abruptly at 

 the under tail-coverts, which are pure white, in marked contrast to the rest of the under parts ; 

 lining of wings and axillars also pure white. Winter plumage of adult : Differs from the 

 above chiefly in the color of the cap ; forehead white ; crown white, but marked with narrow 

 shaft-lines of black, which increase from before backward until, on the nape, the black is 

 nearly or quite pure. A lateral stripe, more or less pure and distinct, extends forward on 

 sides of head over the auriculars, to just in fi-ont of eye, leaving, however, the eyelids white. 

 Upper parts much as in summer, but under parts from chin to vent, much lighter. The 

 carmine of bill and feet lighter and duller, but not the coral-red tint of the feet of hirundo or 

 forsteri. Plumage of the young-of-the-year : BiU much smaller than in the adult, being 

 only l.OS inches long ; brownish-black toward tip ; gonys and sides of lower mandible toward 

 the angle of the mouth dull orange ; feet only orange -colored on the soles, otherv^use brownish- 

 red. Tail much shorter than in adult, only 4.75 to 5.00 inches long, and the outer pan- 

 of rectrices broader and scarcely at all tapering in form. Forehead white; the crown 

 streaked with narrow, longitudinal spots of white upon a black ground color, which extends 

 as far as the eyes, and runs back over the temples and auriculars as far as the nape. Whole 

 under parts from the chin, including under tail-coverts and under surfaces of wings, pure 

 white. On the back there predominates everywhere a uniform, light bluish-gray (somewhat 

 darker than in S. hirundo), all the feathers tipped with yeUowish- white or white, most of 

 them with a blackish-brown streak or crescent-shaped spot near the end ; these spots darkest 

 on the tertials and inner secondaries, and aggregated into a single, broad, slate-colored streak 

 on the least wing-coverts. The ashen-blue primaries deepen into slate-color toward their 

 tips ; their shafts white, their inner webs with a longitudinal space of white, the outer web 

 of the first slaty-black. Inner tail-feathers white, as are their shafts ; their tips white, each 

 with a subterminal crescent-shaped spot of brownish-black. Dimensions of the adult: 

 length (extremely variable from varying length of taU) 14.00-17.00 inches ; extent 29.00- 

 33.00; wing 10.00-10.75; tail usually 7.00-8.00, sometimes 6.50-8.50; depth of fork 4.00- 

 5.00; tibiae bare 0.45; tarsus 0.55-0.65; middle toe and claw 0.80-0.85; inner toe and 

 claw 0.55; whole foot about 1.50; bill along culmen 1.20-1.40; height at base 0.30; 



