The primary purpose of this study was to provide accurate diagnoses of the littoral marine isopod crustacea in the Dillon Beach area. Such a purpose involved a much more complete study of the anatomy of the species represented in the fauna than was heretofore performed. Certain anatomical structures deemed by earlier writers as specifically diagnostic are demonstrated to be unreliable and in a great many instances other structures previously neither described or figured by American writers are considered of paramount importance in species identification. The number and magnitude of the changes proposed in this paper as illustrated in outline form in the summary of the thesis are a sufficient indication of the scientific significance of this study
