LONGIPENNES: LONG-WINGED SWIMMERS. 973 



but Eot of Brandt, 1837, from which distinguished as P. americanus by Grant, Bull. 

 B. 0. C. No. xlix, Dec. 29, 1897, p. xxiii ; Cat. B. Brit. Mus. xxvi, 1898, p. 456; A. 0. U. 

 Suppl. List, Auk, Jan. 1899, p. 102, No. 112. 



P. rubricau'da. (Lat. rubricauda, red-tail ; richer, red ; ccmda, tail.) Red-tailed Tropic 

 Bird. Tail of 16 feathers. Adult ^ 9 : Bill orange; iris black; tarsi and bases of toes 

 bluish, rest of toes black. Plumage pure white, with a delicate roseate hue in high feather. 

 A black transocular fascia, as in other species. Outer primaries with outer webs white. Inner 

 secondaries with au irregular black band ; remiges and lateral rectrices with most of the shafts 

 black on upper side to near end ; long middle tail-feathers carmine or scarlet, fading to white 

 toward the base, with stiff black shafts, and a narrow black edging next them on the very 

 slender webs ; flank-feathers with blackish stripes. Young : Bill black or blackish, gradually 

 changing to orange ; upper parts with more black than in the adults, in bars on most of the 

 upper parts, in spots and lengthwise stripes on the remiges and rectrices. Large : Length 

 about 36.00; wing 12.25-13.25; long tail-feathers about 18.00; tarsus 1.25; bill 2.50-2.60. 

 Tropical and subtropical Pacific and Indian Oceans : a recent addition to our Fauna, new to 

 the Key: one specimen taken near Guadalupe Island, California, July 23, 1898 (Anthony, 

 Auk, Jan. 1898, p. 39). P. ruhricauda Bodd. 1783; A. 0. U. Suppl. List, Auk, Jan. 1899, 

 p. 102, No. [113.1]. P . phoenicurus Gm. 1788. P. melanorhynchus Gm. 1788 (young). 



Order LONGIPENNES: Long-winged Swimmers — Jaegers, Gulls, 



Terns, Skimmers. 



Long-winged Natatores with open lateral nostrils and small free hind toe. Wings long, 

 pointed, reaching when closed beyond base, in many cases beyond end, of tail, which is usu- 

 ally lengthened and always of 12 rectrices. Tail square, or square with long-exserted middle 

 feathers, or forked, or forficate, exceptionally cuneate. Developed primaries 10; no 5th sec- 

 ondary (wings aquintocubital). Legs more or less perfectly beneath centre of equilibrium when 

 the body is in the horizontal position; crura more nearly free from the body than in other 

 Natatores, if not completely external ; tibiae naked below ; tarsus scutellate in part, elsewhere 

 reticulate. Anterior toes palmate ; hallux never united with the inner toe, highly elevated, 

 directly posterior, very small (rudimentary in Rissa). Bill of variable form, but never exten- 

 sively membranous nor lamellate, the covering horny throughout, sometimes discontinuous. 

 Nostrils pervious, lateral, slit-like, but never abortive. No gular pouch. Altricial and nidi- 

 colous, but young covered with down when hatched. Eggs oftenest 3, always colored ; nest 

 ordinarily on the ground or rocks. Chiefly piscivorous. 



Palate schizognathous ; maxillo-palatines lamellar and concavo-convex ; basipterygoid 

 processes wanting; nasal bones schizorhinal. Cervical vertebrfe 15. Sternum singly or 

 doubly notched on each side of the posterior border ; furculum with a hypocleidium ; coraco- 

 humeral groove well marked; hypotarsus with two grooves. There is apparently one pair 

 of syriugeal muscles throughout the order ; oesophagus capacious and distensible ; no spe- 

 cial crop ; proventriculus is a bulging of the gullet ; gizzard small and little muscular ; coeca 

 variable; cloaca large. Contour-foathors aftershafted ; oil-gland tufted; spinal pteryla de- 

 lined in neck by lateral apteria, forked on back. According to Nitzsch, the pterylosis of Gulls 

 •' a])proachps very closely that of the Scolopacidce, and can hardly be distinguished therefrom 

 with certainty by any character." In Terns, " in consequence of the slender and elegant form 

 of the body, the tracts are very narrow, and perfectly scolopacine." Jaegers differ " in having 

 the outer branch of the inferior tract united with the main stem in the first part of its course, 

 and all the tracts still broader and stronger than in " Gulls. With all due regard to the 



