This is apparently a smaller species than _longa_ or _robusta_ and is composed of fewer segments. It differs from those species in having the anterior division of the body composed of only nineteen segments and in having the first branchiæ appear on the thirteenth or fourteenth segment. The prostomium is broadly subtrapeziform, narrowing forward and with the anterior margin varying from slightly convex to mesally indented as is the case in the type; dorsal surface nearly flat, simply marked with two furrows, or sometimes with the median caudal region between furrows elevated. Peristomium with anterior margin above more or less concave, its median length about equal to that of the second segment, which is also ordinarily bowed caudad. In the neuropodia of the anterior region the postsetal processes are broad, distally rounded, thick lips which are prominent; in the posterior region these become narrowly conical, elongate, distally pointed processes. The postsetal processes of the notopodia in the anterior region are thick, short cones which increase in length in going caudad, in the posterior region being very elongate. The branchiæ begin on the thirteenth or fourteenth segment as short processes but become abruptly longer, basally thick and distally pointed processes much thicker than the postsetal processes of the notopodia and exceeding these in length; they are widely separated and, while curving in somewhat mesad, do not come in contact, leaving much of the middorsal region naked. They continue to the end of the body. The neuropodial setæ of the anterior region are arranged in three subvertical series and form a patch twice as high (dorsoventrally) as long (cephalocaudally). The stout setæ of the posterior row are mostly four in number, less commonly three or five. These coarse setæ are not at all clavate as in elongata and are not roughened or cross-ridged above the curve as in robusta; the terminal region above the curve longer than in the later species. The setæ of the other series are more curved than in robusta and are abruptly contracted farther from the body, the contraction stronger but the one edge similarly roughened or denticlated with cross lines. At the ventral end of the series a small patch of ordinary, camerated, capillary setæ resembling the notopodials. The body is broad anteriotly and narrows to the posterior end. Dorsal surface flat and the ventral convex as usual. Number of segments in the type one hundred and thirty-six. Color in general pale brown; at black spot at base of each branchia at least those of posterior region, in front and behind and the proximal part of branchia often darkened. Length, 27 mm.; greatest width, 2.4 mm. Type--M. C. Z. 2, 161. _Scoloplos acmeceps_ sp. nov.