While examining a number of Limnoria lignorum (Rathke) living in a piece of cork washed ashore at Zandvoort (Netherlands), Mr. J. H. Stock found attached on abdomen and legs of these Isopods some Ostracods belonging to the family of Cytheridae. As the specimens, though having characters in common with some known genera, differ markedly, I propose to establish 2 new genera, viz. Aspidoconcha and Redekea. Dr. W. Vervoort [1950, Harrietella simulans (T. Scott, 1894). A commensal Copepod on Limnoria lignorum (Rathke), Zool. Meded. 30 (20) mentioned the presence of Ostracods on Limnoria lignorum collected by Mr. J. A. W. Lucas in a piece of wood washed ashore near Katwijk. Through the kindness of Prof. Dr. H. Boschma, director of the Leiden Museum of Natural History I was able to study the Ostracods. These proved to belong to the same species as the specimens of Aspidoconcha found by Mr. Stock. In vain I examined the autochthonous Limnoria lignorum material in the collections of the Zoological Museum, Amsterdam, for the presence of Ostracods.