Palpal processes lost from type. Proboscis as protruded short, distally expanded over proximal region. Parapodia dorsolateral in position, the anterior ones very thick. Principal postsetal lobe rising above into a branchial process which is short anteriorly but in posterior region is much longer, slender and subulate. Mesad of the branchial process of each parapodium of the first four pairs is a cirrus or cirriform process. The inferior setæ of the most anterior parapodia' much shorter than the dorsals, strongly curved. In the first notopodial fascia a much stouter, aciculiform, setæ which is uncate. Crochets with strongly narrowed neck; with two curved teeth at distal end above the beak which is decurved; in posterior region few in number, commonly four in a series. Anal cirri slender, filiform, much longer than the preceding branchiæ; one in the type has a short spur near its base. Total number of segments about one hundred and sixteen. Length, 21.5 mm. Type--M. C. Z. 2, 165. Balboa. The tubes adhere closely to the body. Their walls of fine sand. AMPHARETIDÆ _Schistocomus_ gen. nov. Like Phyllocomus in lacking tentacles and postbranchial spines, in bearing fifteen pairs of fasciæ of capillary setæ and four pairs of branchiæ. It differs from that genus in having the branchiæ of two types, one pair being of the ordinary, smooth, simple, subulate form and the other three with the edges divided, two pinnately, bearing two close series of lamellar branches, and one with an essentially single series of branches in the genotype. _Genotype_--_S. hiltoni_ sp. nov. _Schistocomus hiltoni_ sp. nov. The body has the ordinary general form, being widest near the fifth setigerous segment from where it narrows continuously to the slender, pointed cauda. Dorsum convex, venter less so, the latter with a double median longitudinal furrow in the posterior region. Prostomium projecting forward as a simple hood with rounded anterior corners and the median region of anterior edge nearly straight; dorsal surface in type longitudinally wrinkled. Ventrally the peristomium projects forward between the sides of the prostomium in a conspicuous lobe or lower lip which narrows somewhat distad and has the distal margin convex; surface longitudinally wrinkled. Second somite achaetous. The third bearing the first fasciæ of simple setæ, the sixth the first uncini. Of the pinnate branchia one pair occur on the third setigerous somite and one on the second while the branchiæ with single series of branches in which the branches are less lamellate, are on the second (first presetal) somite, the simple branchiæ arising on the first setigerous somite. The first branchiæ are attached near the middle of the dorsum, the others laterad close above the parapodia. The first and especially the second or simple branchiæ extending forward beyond the anterior edge of the prostomium. Color light fulvous or in part greyish. Number of segments near fifty-five.