one in the anterior region is stoutest, but becomes more slender in the posterior region. Both notocirri and neurocirri proportionately very slender. Anal cirri about as long as the dorsal tentacular cirri, flattened. Number of segments, sixty-two. Length of types, 20 to 23 mm. Type--M. C. Z. 2, 152. Taken among hydroids. _Nereis mediator_ sp. nov. This species also resembles _N. vexillosa_, though apparently a normally much smaller form. It is, so far as evidence at present accessible to me indicates, distinguishable from that species in having a narrow band across the anterior border of the dental band of VII composed of much finer denticles instead of having the anterior teeth large and the posterior ones reduced. The paragnatha are fewer than in _vexillosa_, those of II, e. g., being in fewer (usually three), less oblique and more separated series and those of VI in all the typical specimens being three in a triangle or four instead of from six to nine or more in a crowded patch. No colored markings. The tentacles proportionately thicker and obviously closer together. Tentacular cirri shorter. Notocirral laminae of the middle and posterior regions much less elongate and flattened with their ventral conical lobe much more pronounced throughout, more as in the smaller specimens of _vexillosa_. Anal cirri short. Number of segments up to seventy. Length, to 60 mm. Type--M. C. T. 2, 153. This is doubtless the same form as recorded by Dr. Moore from San Diego as _N. vexillosa_ in Proc. Acad. Sci. Phil., 1909, p. 244. It is undoubtedly close to that species; but as all the specimens which I have seen, and apparently also those studied by Moore, differ constantly in the features above mentioned from specimens of _vexillosa_ from more northern localities on the Pacific coast, etc., the form is maintained as distinct. A single heteronereis female is among the specimens from Laguna Beach. LEODICIDÆ _Leodice monilifer_ sp. nov.