In erecting Lepeophtheirus semicossyphi YAMAGUTI the original author (1939) gave the definition of the species on the basis of the adult and juvenile females obtained from the gills of Semicossyphus reticulatus VALENCIENNES. Although he mistook the juvenile females for the males at that time, he and Y AMASU (1959) discovered the true males later and issued a detailed description of this sex, making in addition some rectifications to the previous diagnosis of the female. Recently, through the courtesy of Dr. T. ToKIOKA of Seto Marine Biological Laboratory, I had an opportunity to study a number of specimens of this species taken from the fishes kept in the water-tank of Shimonoseki Aquarium. On closer examination of both the sexes it proved that the original descriptions and figures leave something to be desired, especially with respect to the characters of the female. A brief account based on the present specimens will be given here as a supplement. According to the description on the label attached to the vial, the specimens were found at least on three species of fishes inclusive of the type host. This may probably be due to the accidental migration of the parasites from the legitimate host to other kinds of fishes which were kept in one and the same aquarium.