Resembling _S. armiger_ (O. F. Müller) in general structure. A less deeply pigmented species easily distinguished from this northern form in wholly lacking the ventral papillæ (neurocirri) present in the latter below the parapodia of about the eighteenth to thirtieth segments. The prostomium is similarly elongate and pointed but is more slender; it is borne at the end of the peristomium which has the form of a truncate cone. The branchiæ begin anteriorly in the same way as very slight elevations and increase quickly to long ligulate forms; but the first one appears on the sixteenth or seventeenth setigerous segment instead of on the twelfth or thirteenth as usual in armiger. The fully developed branchiæ are obviously narrower than typical for the latter species. The lobes of the parapodia are in general similar though they do not become obvious so far forward. In the second division of the body the ventral lobe is similarly elongate and bifid at the tip with the inner or more dorsal lobe the longer; but the lobes are characteristically more divergent, thinner and more slender. The first bifid neuropodial lobes appear on the twenty-first setigerous segment. The dorsal lobe similar in form to that in armiger. Caudal end of all the types missing. Greatest width, 2 mm. Type--M. C. Z. 2, 162. Balboa (Sept. 10, 1917). FLABELLIGERIDÆ _Flabelligera haerens_ sp. nov. This species resembles _F. commensalis_ Moore in the approximation of the neuropodia though these are apparently not so close as in that species and are at no place actually contiguous though nearly so in the extreme caudal region. In front of this they remain a uniform distance apart, which is less than the length of a somite, forward to about the tenth somite from where the rows diverge gradually forward. The notopodia more widely separated, the rows diverging cephalad from near the tenth somite, always much closer to each other than to the neuropodia. Ventral surface flattened or weakly concave, the dorsal surface also flattened but slightly convex, while the sides are convex; the body in part is slightly compressed from side to side, in cross-section subquadrate to subcircular; widest in middle region and narrowing both ways, more strongly so caudad, subfusiform. Collar lobe deeply and widely incised dorsally and ventrally; the lobe on each side bearing a series of numerous long cross-striated setæ which are reddish brown in color and are stouter than the ordinary notopodials. The notopodials are simple, finely tapered, colorless setae. There is a single seta in each neuropodium, this being in the form of a very stout hook; the color is dark throughout; the transverse terminal portion of the hook is longer and more slender and acute than in commensalis and the pseudo-joint is farther proximad of the curved region; the shaft is bent caudad at the level of the joint, the hook proper curving mesad. The entire surface is densely papillose. The setæ of the collar are