One of the specimens dealt with in the present paper has been described in previous papers, in which it appeared under three different names, all of which for different reasons eventually proved to be erroneous. The present identification as Sacculina cordata Shiino at last seems to be definite. The second specimen, as the first from the material collected by the Siboga Expedition, belongs to the species Sacculina papposa V. K. & B., of which up till now the type specimen only was known; the parasite dealt with here is interesting because the excrescences of its external cuticle are of a structure slightly different from that of the corresponding parts in the type; moreover, in this specimen retinacula were found, yielding an additional character for the definition of the species. The remainder of the material dealt with here proved to belong to a new species, characterized in the first place by the peculiar excrescences of the external cuticle.