A species characterized by its rather thin, easily detached elytra which have their surface wholly smooth or, at most, showing a few scattered minute points; closely fringed along the outer margin, about the cephaloectal region, and for a short distance along the anterior edge. Elytrophore attached cephaloectad of middle. Anterior and ectal margins of a typical elytron only weakly convex, the cephaloectal corner subrectangular though rounded; caudal margin strongly convex, the inner end of elytron like the end of an ellipse but with lower margin the more oblique. Elytra transverse or but little oblique, strongly overlapping in the middorsal line. Prostomium of usual general form. Eyes large and black, the anterior ones near middle of main region of prostomium, the posterior ones closer together and at caudal end. Only one tentacle, a lateral, retained in type. This characterized by a short cylindrical style which to the base of the distal swelling is scarcely longer than the basal process, and especially by an unusually long slender tip which is as long as the rest of the style. The parapodium of the first segment bears two prominent setae in the usual position; tentacular cirri of usual form, the filiform tips long, when bent back reaching proximad of middle of style. Notocirri also characterized by their long terminal filaments. Neuropodial setae light amber-colored; arranged in the usual vertically elongate patch, presenting a narrow dorsal half and a broader ventral one. In the ventral part of the patch normally four longitudinal rows of three setae each, while the narrower upper region shows also about four rows but with only two or one in each. The setae have the usual general structure. Notopodials numerous, reaching beyond distal end of neuropodia and sometimes nearly to middle of the neuropodial setae. In the type the elytra are light brown. The tentacles and notocirri ringed with black as common. Length, 13 mm.; width exclusive of parapodia, 3 mm.; width to tips of setae, 6 mm. Dredged. Type--M. C. Z. 2, 142. PHYLLODOCIDAE _Hesperophyllum_ gen. nov. Similar in general to _Notophyllum_ and _Austrophyllum_ but differing especially in having the ventral cirrus of the second segment flattened and foliaceous and strongly asymmetrical. It is like _Notophyllum_ and unlike _Austrophyllum_ in having the first segment dorsally reduced. _Genotype._--_H. tectum_ sp. nov. _Hesperophyllum tectum_ sp. nov.