.I have confirmed in the main the accounts of Braun, Linton, and Southwell of the two remarkable species, ľolypocephalus medusia and P. radiatus, and have contributed some additions. The chief of these are the presence in P. medusia, as in P. radiatus, of an opening (borne on a central column) from a glandular mass situated under the floor of the tentacle-containing hollow or cavity, the alternation of the dorsal and ventral surfaces of proglottis with genital pores on opposite sides, the quadripartite form of the ovary, and of the columns of vitellaria, which are continuous, anteriorly and posteriorly, with it. Comparison of the strobilæ of the two species shows that they undoubtedly belong to the same genus–the general disposition of the organs, number of testes, and origin of the uterus being the same in both, –a, conclusion obviously suggested by the similar form of the scoleees. The two species, on the other hand, are very distinct from each other. The arrangement of the vitellaria in four columns (if the vitellaria be represented by these extensions of the ovary) is, so far as I know, unparalleled among Cestoda, The genus Polypocephalus is re-defined and the two species diagnosed.