1882,] FKOM 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 speci- 

 men, which is a fully adult and a freshly-moulted example. The dis- 

 tinctions 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 ut a glance at any age. It is substantially correct 

 to define the northern R. nigra as a white-tailed, and the southern 

 It. melanura as a black-tailed bird. In the winter plumage both 

 species show a more or less defined white collar. 



There is a break in the chain of evidence respectiug the inter- 

 tropical range of tliese two species. Through the kindness of my 

 friend Mr. E. Hargitt, I have specimens of the souiliern form, R. me- 

 lanura, 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.) 

 Zaras/Mrea^MS, Neboux, Voy. 'Venus,' Atlas, pi. x. (1846), descr. 

 Rev. Zool. 1840, p. 290. 



Creagrus furcatus, 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, Gala- 

 pagos 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 auri- 

 cular patch as in most of the immature hooded Gulls ; neck and 



