LABID^ — STEENIN^ : TEBNS. 756 



rous, and flutter about over marshy spots like swallows or night-hawks. The general appear- 

 ance and mode of flight have suggested the name of " sea-swallow," the equivalent of which 

 is applied in nearly all civilized languages. A forking of the tail is an almost universal char- 

 acter. In the Caspian and marsli terns, the black tern and its allies, and some others, the 

 forking is moderate, and not accompanied by attenuation of the lateral feathers ; but ordi 

 narily, these are remarkably lengthened and almost filamentous, as in the barn swallow. It 

 -should be observed that in all such cases the narrowing elongation is gradual, and consequently 

 less evident in the young ; and that it is very variable in its development. The noddies offer 

 the peculiarity of a tail lightly forked centrally, but rounded laterally. The feet are small and 

 relatively weak throughout the group ; the terns walk but little, and scarcely swim at all. 

 Ordinarily the webbing is rather narrow, and incised, particularly that between the middle and 

 inner toe ; in Hydrochelidon, this occurs to such extent that the toes seem simply semipalmate. 

 The webs are fullest in Aiioiis, where also the hallux is unusually long ; in some species, this 

 toe is slightly connected with the tarsus by a web. The iuner toe is shorter than the outer, 

 and much less than the middle, which, especially iu Hydrochelidon, is much lengthened, and 

 lias the inner edge of its claw dilated, or even slightly serrate. The coloration is very con- 

 stant, almost throughout the subfemily. Most of the species are white (often rosy-tinted be- 

 low), with a pearly-blue mantle, a black cap on the head, and dark-colored primaries, along 

 the inner Aveb of which usually runs a white stripe. These dark-colored quiUs, when new, are 

 beautifully frosted or silvered over ; but this hoariness being very superficial, soon wears off, 

 leaving the feathers simply blackish. The black cap is often interrupted by a white frontal 

 crescent ; it is sometimes prolonged into a slight occipital crest ; iu a few species, it is replaced 

 by a black bar on each side of the head. One species, Inca mystacalis, has a curious bundle of 

 curly white plumes on each side of the head. Another, Gygis alba, is pure white all over; 

 Procelsterna cinerea is wholly ashy ; the noddies are all fuliginous ; the upper parts of Hali- 

 plana are dark ; the species of Hydrochelidon are largely black. These are the principal if 

 not the only exceptions to the normal coloration just given. The sexes are never distinguish- 

 able, either by size or color ; but nearly aU the species, iu the progress toward maturity, 

 undergo changes of plumage, like guUs; while the seasonal differences are usually consider- 

 able. As a rule, the black cap is imperfect iu young and winter specimens, and the former 

 siiow gray or brown patching instead of the pure final color of the mautje. In all those species 

 iu which the bill is red, orange, or yellow, it is more or less dusky iu the young. The changes 

 are probably greatest in the black terns. 



The general economy is much the same throughout the group. The eggs are laid in a 

 slight depression on the ground, — generally the shingle of beaches, or in a tussock of grass in 

 a marsh, or in a rude nest of sticks iu low thick bushes ; they are 1-3 in number, variegated 

 in color. Most of the species are maritime, and such is particularly the case witli the noddies ; 

 but nearly all are also found inland. They are noisy birds, of shrill penetrating voice ; and no 

 less gregarious than gulls, often assembling iu multitudes to breed, and generally moving in 

 Cijmpauy. Species occur near water in almost every part of the world, and most of them 

 are widely distributed ; of those occurring iu North America, the majority are found in corre- 

 sponding latitudes in the Old World. Some seventy species are currently reported ; the true 

 number is apparently just about that of the Gulls (about fifty). 



The generic and subgcneric groups of the Sternirue are rather better marked than those 



of the Larin(B. Phtethusa, Gygis, and several subgenera near Anous are extralimital. The 



North Ameiicau forms may readily be distinguished by the following analysis. Hydrochelidon 



and AnoUs may be regarded as genera, the remainder being subgenera of Stertia. 



Analysis of the North American forms of Sternina. 



Nostrils sub-basal. Frontal antias prominent, embracing base of culmen. Tail more or less forked. 



Tarsus not shorter tban middle toe without the claw. Lateral toes much shorter than the middle. 



