The Rhizocephala of the Leiden Museum

In the paper on the Rhizocephala of the Siboga Expedition ( VAN KAMPEN and BOSCHMA 1925) besides the material collected during this expedition a number of specimens from other collections have been described. Among these there were a few from the collection of the Leiden Museum ('s Rijks Museum van Natuurlijke Historie). The rich collection of Crustacea in this Museum, however, contains a much larger number of specimens infested with Rhizocephala than those described in the cited paper, as turned out after an inspection of the whole collection. Alltogether 35 specimens, including the 10 specimens described in the cited paper, could be found. The taxonomy of the Rhizocephala is a rather difficult problem, which can be solved only after the study of a comparatively large material. The differences between the genera of this group of parasites are strikingly enough (cf. SMITH 1906), but within each genus the species usually differ in subordinate characteristics only, the internal anatomy of the species of each genus usually showing a close resemblance. The chief characteristics of the species, especially in Sacculina and allied genera, are those of the chitinous parts of the mantle: the excrescences of the external cuticle and the retinacula. KOSSMANN (1872) discovered the excrescences of the external cuticle in many Sacculinidae from the Philippine Islands and by means of these excrescences he was able to describe several species. Many of these species are well defined and we could identify a certain number of specimens from the East Indies with some of KOSSMANN'S species (cf. VAN KAMPEN and BOSCHMA 1925). In the cited paper we moreover proved that in certain cases also the