The other neurocirri much shorter, subconical, constricted at base and prolonged into a slender but short tip; attached near base of neuropodium in each case. Anal cirri similar to notocirri but much longer and stouter. Neuropodial setae of usual general form, amber colored with dark tip, arranged mostly in two or three, usually uneven, subvertical series. The notopodial setae fine, numerous, the longer ones not falling much short of or reaching the ends of the neuropodials. The nephridial papillæ occupy the ordinary position; they are small and unusually short. The color of the elytra uniform greyish brown. Antennæ, tentacular cirri and notocirri banded at base and distally with black. Length, 23 mm.; width exclusive of parapodia, 3 mm. A little narrowed cephalad, somewhat more so caudal. Taken at Laguna Beach under stones. (1917) Type--M. C. Z. 2, 139. _Halosydna leioseta_ sp. nov. Body strongly and continuously narrowed caudad. Prostomium wider than long, deeply bilobed, the median tentacle inserted deeply in the intervening incision. Lobes extended forward into peaks which, however, are constricted at base so as to give appearance of more or less distinct ceratophores, these short. Anterior eye free on each side, the caudal one much farther mesad and overlapped by the peristomium. Tentacles short, the median line a little longest and about equalling the palpi; in each a slender tip above the moderate subdistal swelling about equal in length to the remaining part of the style. Tentacular cirri similarly formed, as is also the first neurocirrus, the latter less clavate below the slender tip. Other neurocirri much shorter, shortly subfusiform with filiform tip short; characteristically inserted almost precisely at middle of length of the neuropodium. Notopodia reduced to small lobes at base of neuropodia above, these lobes smooth, bearing no emergent setae in the type. In the average neuropodium the setae are mostly six in number; these are coarse, with subhastate heads the tips of which are curved, entire, and acute; the surface appears smooth, the seriate spinules being exceedingly minute and easily overlooked; pale straw colored. The notocirri have the usual enlarged distal end baring a slender tip and a little exceed the neuropodial setae. The elytra have an arrangement in general similar to that normal in Halosydna so far as that usually goes, but twenty-four pairs are present, these occurring on somites, II, IV, V, VII, IX, XI, XIII, XV, XVII, XIX, XXI, XXIII, and XXVI, XXVIII, XXIX, XXXI, XXXIII, XXXV, XXXVII, XXXIX, XLI, XLIII, XLV, and XLVII. The elytra are characteristically widely imbricated so as completely to cover the dorsum and prostomium. They extend out far laterally so as wholly to overlap the parapodia proper though the ends of the setae and notocirri extend beyond the edges. The elytra have the surface wholly smooth and the edges are also not fringed. As preserved, the type has no definite