Of the great American family Trochilidæ, which, according to the most recent authorities, contains about 450 species, eleven members have been ascertained to occur within the limits of the Argentine Republic. But of these only three (_Calliperidia furcifera_, _Hylocharis sapphirina_, and _Chlorostilbon splendidus_) reach the neighbourhood of Buenos Ayres, where they occur as summer visitors. The remaining eight have been met with only in the northern and western provinces of Argentina. Of these two (_Oreotrochilus leucopleurus_ and _Patagona gigas_) are also found in Chili, the others are Bolivian and South-Brazilian species. 230. OREOTROCHILUS LEUCOPLEURUS, Gould. (WHITE-SIDED HUMMING-BIRD.) +Oreotrochilus leucopleurus+, _Scl. et Salv. Nomencl._ p. 81; _White, P. Z. S._ 1882, p. 615 (Catamarca); _Elliot, Syn. Troch._ p. 36; _Gould, Mon. Troch._ ii. pl. 71. _Description._--Head, upper surface, and wings greyish olive-brown, passing into dull coppery green on the upper tail-coverts; two central tail-feathers and outer one bronzy green, the others white, narrowly edged externally with brown; throat shining green, bordered below by a band of black with bluish reflexions; flanks olive-brown; breast and sides of belly white; centre of belly black with steel-blue reflexions; under tail-coverts olive: whole length 5·0 inches, wings 2·7, tail 2·1. _Female_ above like male; beneath white, throat densely spotted with brown; flanks brownish. _Hab._ Chili and Northern Argentina. White obtained a single specimen of this Humming-bird in September 1880, at Fuerte de Andalgala, in Catamarca. It is a well-known species in Chili, where, according to Gould, "it inhabits the sheltered valleys of the Andes, just below the line of perpetual congelation." 231. CHÆTOCERCUS BURMEISTERI, Scl. (BURMEISTER'S HUMMING-BIRD.) [Plate XI.] [Illustration: CHÆTOCERCUS BURMEISTERI.] +Chætocercus burmeisteri+, _Scl. P. Z. S._ 1887, p. 639.