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Show 1882.] FROM PERU AND CHILI. 523 upper and under sides are dark smoke-colour, with merely a thin outside margin of a lighter tint; the under wing-coverts are dusky; the tips of the secondaries show far less white than in the northern bird ; whilst the upper primaries can hardly be said to show any trace of lighter colour even in this Coquimbo specimen, which is a fully adult and a freshly-moulted example. The distinctions admittedly rest upon the respective preponderances of light and dark; and in the immature northern bird, such as I consider the Central-American example to which reference has been made, the tail is not so white as in the adult; nevertheless the two forms can be separated at a glance at any age. It is substantially correct to define the northern R. nigra as a white-tailed, and the southern R. melanura as a black-tailed bird. In the winter plumage both species show a more or less deflned white collar. There is a break in the chain of evidence respectiug the intertropical range of these two species. Through the kindness of my friend Mr. E. Hargitt, 1 have specimens of the southern form, R. melanura, from as far north as Berbice, British Guiana, about lat. 6° N.; and it probably ascends the Orinoco, and passes along the coast of Venezuela. In this case the northern range of R. melanura in the Atlantic would come very close to the territory of the northern R. nigra, which is common in Florida, whence I possess examples. Under these circumstances the wonder is that the distinctions between the northern and southern forms should be so marked as they are. XEMA FURCATUM (Neboux). (Plate XXXIV.) Larus furcatus, Neboux, Voy. 'Venus,' Atlas, pl. x. (1846), descr. Rev. Zool. 1840, p. 290. Creagrusfurcatus, Bp. Naum. 1854, p. 213; Salvin, Tr. Z. S. ix. p. 506. Xema furcatum (Neboux), Saunders, P. Z. S. 1878, p. 210. [No. 9, Paracas Bay, Peru, Oct. 1881. Eyes brown.] The third known example of this rarest of Gulls, the history of which may here be briefly recapitulated. The Paris Museum possesses one, in somewhat immature plumage, said to have been obtained by Dr. Neboux, of the French frigate ' Venus,' at Monterey, California, in the month of November. The British Museum has an adult in full breeding-plumage, obtained during the voyage of H.M.SS. ' Herald ' and ' Pandora,' at Dalrymple rock, Chatham Island, Galapagos group, nearly on the equator, between the 11th and 16th January. It is a medium-sized Gull, with long wings (16 inches), a dark slate-coloured hood, and a forked tail; indeed were it not that the hood is separated from the base of the hill by a band of white feathers, and that there is no black neck-ring at the base of the hood, Xema furcatum might be described as a gigantic Sabine's Gull. In the young, now figured, the resemblance to the young of Xema sabinii is very marked. The entire head is white, with dark markings in front of and surrounding the eyes, and a brown auricular patch as in most of the immature hooded Gulls ; neck and |