This species, which, on close comparison, is at once distinguishable from _S. modesta_ by the absence of any black colour on the three exterior pairs of tail-feathers, ranges from the extreme north of the Argentine Republic to Patagonia, where it is quite common, and is invariably found in dry situations abounding in thorny vegetation. It does not migrate, and lives with its mate in thorny bushes, but does not attempt to conceal itself, and sits much on the summit of a bush, where the male in spring utters at intervals a clear trilling call. In its inactive disposition, slow deliberate movements, also in its language, it strikingly resembles the _Phacellodomus ruber_. In its nidification it also comes nearest to that species. The nest is a large structure of sticks, eighteen inches to two feet long, placed upright among the twigs at the summit of a bush. From the top where the entrance is placed, a winding passage leads down to the chamber at the bottom of the nest; this is lined with soft dry grass and feathers, and four pure white eggs are laid. 201. SYNALLAXIS SULPHURIFERA, Burm. (YELLOW-MARKED SPINE-TAIL.) +Synallaxis sulphurifera+, _Hudson, P. Z. S._ 1872, p. 544 (Rio Negro); _Scl. et Salv. Nomencl._ p. 64; _Scl. P. Z. S._ 1874, p. 24; _Durnford, Ibis_, 1877, p. 180, et 1878, p. 61 (Buenos Ayres); _Barrows, Bull. Nutt. Orn. Cl._ viii. p. 208 (Entrerios). _Description._--Above brown, slightly olivaceous; wings blackish; lesser wing-coverts, margins of the feathers of the greater wing-coverts, and outer webs of the basal halves of the wing-feathers pale chestnut; tail-feathers chestnut-brown, ends much elongated and pointed; beneath white, throat and breast mottled with grey, spot in middle of throat sulphur-yellow; flanks washed with brown; bend of wing and under wing-coverts fulvous; bill and feet pale horn-colour: whole length 6·3 inches, wing 2·1, tail 3·0. _Female_ similar. _Hab._ South Argentina and Patagonia. I have found this _Synallaxis_, which was first described by Prof. Burmeister, from specimens obtained near Buenos Ayres, in the swamps along the Plata river; also on the Rio Negro, in Patagonia, where, however, it is very scarce. It inhabits the dense rush-beds growing in the water, where the _Limnornis curvirostris_ is also found. It closely resembles that species in habits and language, and also assimilates to it in colour and in the rather long, curved beak, sharp claws, stout body, and short stiff tail. It is stationary, pairs for life, and lives always closely concealed in its chosen bed of close-growing rushes. When a person approaches their hiding-place the two birds creep up to the summit of the rushes, protesting in peculiar, loud, angry rattling notes. The _Limnornis_, which also pairs for life, has precisely the same habit.