LONGIPENNES, LONG-WINGED SWIMMERS.—GEN. 278. 307 
small, linear, but remaining patulous. Tail with the two middle feathers in the 
adult filamentous and extraordinarily prolonged, the rest short and broad. 
The tropic birds resemble a large, stout tern in their general figure; the bill, 
especially, being almost exactly like that of a tern. The principal external 
peculiarity is the development of the middle tail-feathers; the feathering of the 
gular sac and the permanent patulence of the nostrils are other features. They 
are graceful birds on the wing, capable of protracted flight, venturing far from land. 
They are gregarious at all times, and nest in communities along coasts and on 
islands, in rocky places or among low trees and bushes. As implied in their name, 
they are birds of the torrid zone, though i in their extensive wanderings they visit 
Southern seas, and have even been reported from latitude 40° N. There are but three 
well determined species: P. flavirostris (below) ; P. etherews, and P. rubricauda. 
278. Genus PHAETHON Linnzus. 
Tropic Bird. White, satiny, rosy-tinted; long tail feathers reddened, 
black-shafted ; sides of head, wings and flanks varied with black ; bill orange ; 
tarsi yellow; toes and webs black; young with more black on upper parts. 
Wing 11; bill 12-2; tarsus 1; tail 4-5, its middle feathers up to 15-20. 
Gulf Coast, rare or casual. P. ethereus Nurv., ii, 503; Aup., vii, 64, pl. 
427; P. flavirostris Branpt; Lawr. in Bp., 885. . . . FLAVIROSTRIS. 
Order LONGIPENNES. Long-winged Swimmers. 
Wings long, pointed, reaching when closed beyond the base, in many cases 
beyond the end, of the tail, which is usually lengthened and of less than 20 rec- 
trices (oftenest 12). Legs more or less perfectly beneath centre of equilibrium 
when the body is in the horizontal position; the crura more nearly free from the 
body than in other Natatores, if not completely external. “Anterior toes palmate ; 
hallux never united with the inner toe, highly elevated, directly posterior, very small, 
rudimentary or absent; tibize naked below. Bill of variable form, but never exten- 
sively membranous nor lamellate, the covering horny throughout, sometimes dis- 
- continuous. Nostrils variable, but never abortive. No gular pouch. Altricial. 
This order, which may be recognized among web-footed birds by the foregoing 
external characters, is less substantially put together than either of the two preceding 
—not that its components are not sufficiently related to each other, but because the 
essential points of structure are shared to a considerable extent by other groups. 
Thus the osteological resemblances of longipennine birds with loons, auks, and 
plover, are quite close, as noted by Huxley; while the digestive system agrees in 
general characters with that of other fish-eating birds. In some of the lower 
members of the order, the tibia develops an apophysis, as in the loons; while 
even in external characters, one genus at least, Halodroma, resembles the Alcide. 
It is not certain, that the order must not be broken up, or rather enlarged and 
differently defined, to include some of the genera now ranged under Pygopodes. 
The palate has the schizognathous structure; ‘‘the maxillo-palatines are usually 
lamellar and concayo-conyex, but in the Procellariide they become tumid and 
spongy” (Hualey) ; basipterygoid processes may be often wanting, but they are 
certainly present in many more cases than Huxley supposed. There is appar- 
ently one pair of syringeal muscles throughout the order. The cesophagus is capa- 
