Eight species of the almost cosmopolitan Thrush-family are known to occur in the Argentine Republic. Of these, five belong to the widely-spread genus _Turdus_, and are closely similar in structure to our European Thrushes. The remaining three are Mock-birds (_Miminæ_)--a group restricted to the New World, and sometimes considered more nearly allied to the Wrens. They are remarkable as splendid songsters. Burmeister includes in his list a fourth species of _Mimus_ (_M. thenca_), as found in the Mendoza district; but there may be some error in this, as _M. thenca_ is only known to us from Chili west of the Andes. 1. TURDUS LEUCOMELAS, Vieill. (DUSKY THRUSH.) +Turdus leucomelas+, _Scl. et Salv. Nomencl._ p. 1; _Hudson, P. Z. S._ 1870, p. 798 (Buenos Ayres); _Durnford, Ibis_, 1877, p. 166 (Buenos Ayres); _White, P. Z. S._ 1882, p. 592 (Misiones and Corrientes); _Barrows, Bull. Nutt. Orn. Cl._ viii. p. 85 (Concepcion); _Seebohm, Cat. Birds_, v. p. 213. +Turdus crotopezus+, _Burm. La-Plata Reise_, ii. p. 474 (Mendoza). _Description._--Above olive-grey, tinged with brown on the head and neck; beneath pale grey, throat white, more or less striped with brown; middle of belly and crissum white; under wing-coverts and inner margins of wing-feathers fulvous; bill yellow; feet hazel: total length 9·0 inches, wing 4·5, tail 3·7. _Female_ similar. _Hab._ Eastern South America, from Cayenne to Buenos Ayres. The Dusky Thrush is widely distributed in South America, and ranges as far south as Buenos Ayres, where it is quite common in the woods along the Plata river. It is a shy forest-bird; a fruit- and insect-eater; abrupt in its motions; runs rapidly on the ground with beak elevated, and at intervals pauses and shakes its tail; pugnacious in temper; strong on the wing, its flight not being over the trees, but masked by their shadows. It can always be easily distinguished, even at a distance, from other species by its peculiar short, metallic chirp--a melodious sound indicating alarm or curiosity, and uttered before flight--in contrast to the harsh screams and chuckling notes of other Thrushes in this district.