Azara's account of this species is prefaced by the following remarks on the birds of this genus known to him in Paraguay:--"These birds inhabit only the dense and tangled thickets, and never show themselves outside of their hiding-places, except for a few moments in the early morning and in the evening; but at no time do they perch high on the trees, but keep always within a few feet of the earth. They live in pairs; feed solely on insects caught in the bushes which they frequent, or on the ground, on which, however, the bird alights only to pick up its prey, and then returns to the twig to devour it. They are stationary, and fly only from one thicket to another. Many of the species have a similar voice or song, which is singular, powerful, and heard only in the love-season. The call is a trill of a single note rapidly reiterated, and loud enough to be heard half a mile away; the cry being accompanied by vibratory motions of the wings." 224. THAMNOPHILUS CÆRULESCENS, Vieill. (SLATY-BLUE BUSH-BIRD.) +Thamnophilus cærulescens+, _Burm. La-Plata Reise_, ii. p. 472 (Paraná, Mendoza, Tucuman); _Scl. et Salv. Nomencl._ p. 70; _White, P. Z. S._ 1882, p. 614 (Corrientes, Misiones); _Barrows, Auk_, 1884, p. 21 (Entrerios); _Salvin, Ibis_, 1880, p. 361 (Salta). _Description._--Above grey, black on the crown, and a patch of white and black feathers on the middle of the back; wings black, the coverts thickly spotted and the inner webs of the remiges edged with white; tail black, all the feathers, except the middle pair, tipped with white, the outer rectrix on each side has also a long white spot in the middle part of the outer web; beneath cinereous, white on the belly; bill and feet black: whole length 5·6 inches, wing 2·7, tail 2·3. _Female_: above earthy olive-green, yellowish on the crown; wing-coverts and tail as in the male; wing-feathers olive-brown; beneath yellowish olive-grey, brightening into ochraceous on the belly and flanks. _Hab._ Paraguay and Argentina. Mr. Barrows says concerning this species that it is "frequently seen, especially during the winter" (on the Lower Uruguay). A nest, taken November 24th, "was almost precisely like that of our Red-eyed Vireo (_V. olivaceus_), being pensile in the fork of a horizontal spray, only four feet from the ground. It contained three fresh eggs, white, with spots and dashes of light brown." White says that these birds frequent the banks of streams, and have a deep bass call-note, rather mournful and slow. 225. THAMNOPHILUS RUFICAPILLUS, Vieill. (RED-CAPPED BUSH-BIRD.) +Thamnophilus argentinus+, _Burm. La-Plata Reise_, ii. p. 472 (Paraná, Tucuman); _Scl. et Salv. Nomencl._ p. 70; _Durnford, Ibis_, 1877, p. 183 (Buenos Ayres); _Barrows, Auk_, 1884, p. 21 (Entrerios). +Thamnophilus ruficapillus+, _Pelz. Orn. Bras._ p. 79; _Berl. et Jher. Zeitschr. ges. O._ 1885, p. 49.