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Rh : [Premnoplex] brunnescens, Hand-list, iii, 1901, 74, part (Costa Rica; Panamá).
 * [Margarornis] brunneicauda, Ann. Lyc. Nat. Hist. N. Y., viii, 1867, 130, in text (Costa Rica; coll. U. S. Nat. Mus.).
 * Premnoplex brunnescens brunneicauda, Proc. Biol. Soc. Wash., xxi, July 27, 1908, 159 (Costa Rica, Chiriquí and Verágua, Panamá; crit.). — , Ann. Carnegie Mus., vi, 1910, 647 (highlands of Costa Rica, 2,000 ft. to timber-line; crit.).

 Genus ACRORCHILUS Ridgway.

Small wrenlike Furnariidæ (length about 130-140 mm.) with tail about as long as wing (sometimes longer), graduated, the rectrices (12) usually acuminate at tip; tarsus much less than one-third as long as wing; basal phalanx of middle toe not wholly united to outer toe, and tail and wings rufescent and plumage without streaks (except, sometimes, on pileum).

Bill much shorter than head, rather stout, slightly decurved, and moderately compressed, its width at loral antiæ slightly greater than its depth at same point and equal to about one-third the distance from nostril to tip of maxilla; culmen distinctly ridged, gradually and rather strongly decurved from near base, the tip of maxilla not uncinate; maxillary tomium more or less distinctly concave, mandibular tomium similarly convex, both without trace of subterminal notch; gonys nearly to quite straight, not prominent basally. Nostril exposed, posteriorly in contact with loral feathering, narrow (a longitudinal slit), overhung by a broad, convex, membraneous operculum. Rictal bristles absent, and feathers of chin, etc., without terminal setæ. Wing rather large and pointed, the longest primaries exceeding secondaries by about distance from nostril to tip of maxilla; seventh and eighth, sixth, seventh, and eighth, or sixth and seventh primaries longest, the tenth (outermost) about two-thirds as long as the longest, the ninth longer than secondaries. Tail very nearly as long as wing to decidedly longer, graduated for nearly to more than half its length, the rectrices (12) usually abruptly attenuated terminally, sometimes with tips acute (but not denuded). Tarsus much longer than whole culmen, less than one-third as long as wing, stout, very distinctly scutellate; middle toe, with claw, decidedly shorter than tarsus; outer toe, without claw, not reaching to middle of subterminal phalanx of middle toe, the inner toe slightly shorter; hallux about as long as inner toe, but much stouter; basal phalanx of middle toe united for half or more (sometimes for nearly the whole) of its length to outer toe, for nearly as much to inner toe; claws moderate