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There seems to have been no record of fresh-water Polychaeta from Japan as yet, except a few nereids (
Ceratocephale osawai,
Nereis japonica) which were found in brackish water. The species which I am going to describe here belongs to the genus
Lycastis, and is found abundantly in Tamsui River, north Formosa. In many points it is similar to
Lycastis hawaiensis Johnson, but is fairly different from the latter in such important characters as follows:—(1) The structure of prostomium, (2) the length of tentacular cirri and of their basal joints, (3) the length of dorsal cirri, (4) the occurrence of the dorsal bristles and (5) their number. Moreover this is closely related to
Lycastis indica Southern, but differs from it in the following points:—(1) The structure of prostomium, (2) the arrangement of the eyes and the lenses, (3) coloration of the body, (4) dorsal and ventral cirri of the anterior feet, (5) length of dorsal cirri, (6) the number and kinds of bristles, (7) length of anal cirri and (8) the number of the teeth in the jaw.
The type specimen is preserved in the Zoological Department of Taihoku lmperial University. Here I would like to tender my hearty thanks to Prof. K. Hirasaka of the same University for his advice kindly given to me.