_Description._--Above glossy dark steel-blue; lower back and rump cinnamon-rufous; the upper tail-coverts brown, with grey margins; wings black; tail black, with greenish gloss; crown steel-blue; forehead sandy buff; cheeks and sides of face chestnut, spreading to the sides of the hind neck; chin chestnut; the lower throat steel-blue; fore neck, chest, and sides of body and flanks light ashy brown; centre of breast and abdomen white, tinged with brown; under tail-coverts, also under wing-coverts and axillaries, ashy brown: total length 5·3 inches, wing 4·35, tail 2·05. _Female_ similar. _Hab._ South America. This species does not breed in Buenos Ayres, and is only seen there in spring, flying south or south-west, and again in much larger numbers on its return journey in autumn. On the Rio Negro, in Patagonia, I did not meet with it, and suppose its summer resort must be south of that locality; and, judging from the immense numbers visible in some seasons, I should think that they must, in their breeding-place in Patagonia, occupy a very extensive area. They do not seem to be as regular in their movements as other Swallows here; some years I have observed them passing singly or in small parties during the entire hot season: usually they begin to appear, flying north, in February; but in some years not until after the middle of March. They are not seen passing with a rapid flight in close flocks, but straggle about, hawking after flies: first one bird passing, then two or three, and a minute or two later half a dozen, and so on for a greater part of the day. So long as the weather continues warm they journey in this leisurely manner; but I have known them to continue passing till April, after all the summer migrants had left us, and these late birds flew by with great speed in small close flocks, directly north, as if their flight had been guided by the magnetic needle. While flying this species continually utters sharp twitterings and grinding and squealing notes of various lengths. 29. TACHYCINETA LEUCORRHOA (Vieill.). (WHITE-RUMPED SWALLOW.) +Hirundo leucorrhoa+, _Hudson, P. Z. S._ 1872, pp. 606, 845 (Buenos Ayres); _Scl. et Salv. Nomencl._ p. 14; _Durnford, Ibis_, 1877, p. 32 (Chupat), 1878, p. 392 (Central Patagonia); _White, P. Z. S._ 1882, p. 596 (Corrientes); _Barrows, Bull. Nutt. Orn. Cl._ viii. p. 89 (Concepcion). +Cotyle leucorrhoea+, _Burm. La-Plata Reise_, ii. p. 478 (Paraná). +Tachycineta leucorrhous+, _Sharpe, Cat. B._ x. p. 114.