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Lobiger (Lobiger) sagamiensis n. sp. (Text-figs. 1-3) Length about 8mm. Animal narrow and elongated, the tail extending far behind the shell. A pair of auriculate rhinophores. Parapodial lobes 4 in all, very irregular in size, the largest ones distinctly indented to form a number of leaflets on the margin. On the underside the parapodial lobes are studded with small blunt tubercles. The shell is like half of a bivalve. It is thin and colourless. General body-colour grass-green, with browish spots here and there on the surface. The marginal leaflets of the parapodial lobes are also tinged with brown. Radula with 4 teeth in the ascending series, 7 teeth in the descending series, and a heap of these in the ascus. The teeth in the ascending series are all smooth, but these in the descending series have each a row of fine denticles on either side of the blade. Loc.: Misaki, Sagami Bay, shallow water, attached to the green alga, Caulerpa brachypus (Aug. 1951, 1 sp.). The genus Lobiger is divided into 3 subgenera: Labiger s. s., Pterygophysis and Lophopleura; the first named-subgenus contains at present 3 well-established species and two somewhat invalid ones. I think the specimen in hand is closely allied to the Indian species L. (L.) nevilli PILSBRY in the general shape of the prapodial lobes and even in colours (see ELIOT 1906), but it appears to have somewhat a different type of radula teeth. For this reason I have provisionally described it as a new species under the name of L. (L.) sagamiensis.