_Description._--Above greyish brown, lores and slight superciliaries whitish; tail-coverts and tail black, the outer web of the outer rectrix white; below pale greyish white, whiter on the belly and crissum; bill black, with the base of the lower mandible yellowish; feet black: whole length 5·5 inches, wing 3·4, tail 2·4. _Female_ similar. _Hab._ Chili, Patagonia, Bolivia, Peru, and Western Ecuador. Prof. Burmeister met with this species near Mendoza, in the mouths of the large torrents above the city. Durnford found it near the river Sengalen in Central Patagonia in December 1877. 136. CENTRITES NIGER (Bodd.). (RED-BACKED TYRANT.) +Centrites niger+, _Burm. La-Plata Reise_, ii. p. 458; _Scl. et Salv. Nomencl._ p. 44; _Durnford, Ibis_, 1878, p. 395 (Chupat); _White, P. Z. S._ 1882, p. 604 (Buenos Ayres); _Döring, Exp. al Rio Negro, Zool._ p. 42 (R. Colorado); _Barrows, Bull. Nutt. Orn. Cl._ viii. p. 142 (Entrerios, Pampas). _Description._--Above and below deep black: whole of back except the rump and scapularies chestnut; bill and feet black; under wing-coverts and wings below black: whole length 5·0 inches, wing 2·8, tail 1·9. _Female_ above brown, back fulvous red; tail black; below ashy brown. _Hab._ Patagonia, Chili, and Argentina. The little Red-backed Tyrant comes nearest to _Muscisaxicola mentalis_ in habits, but does not perch on bushes and trees, and is less gregarious than that bird. It is the smallest of all those varied members of the _Tyrannine_ family which have abandoned forests and marshes and the pursuit of insects on the wing, to live on the wintry uplands of Patagonia, and on the sterile plains bordering on the Andes. The male is only five and a quarter inches long. The entire plumage of the male is intensely black, except the back, which is bright chestnut. The inside of the mouth and tongue are vivid orange-yellow. The chestnut colour on the female is pale, the rest of the plumage grey, except the quills, which are dark. Its summer home is in the southern portion of Patagonia, but its nesting-habits are not known. In March it migrates north, and is very common everywhere on the pampas throughout the winter. They arrive in small parties of three or four, or in little loose flocks of about a dozen individuals, travelling with a swift low flight. Males, females, and young, grey like the last, arrive together; shortly after arriving the young males become mottled with black, and before leaving acquire the adult plumage. They appear to leave in spring all together, but from a note by Durnford it would appear that the males travel in advance of the females. He says:--"Males of this species were common at Chupat throughout September and during the first few days of October. On the 5th of the latter month I observed the first females, which gradually increased in number."