Page:A Revision of the Families and Genera of the Stylonuracea (Eurypterida).djvu/8

Fig. 96. Diagrammatic outlines of the metastomas of most of the families of the Stylonuracea (excluding Carboniferous and Permian families): 1, Dolichopteridae; 2, Stylonuridae; 3, Drepanopteridae; 4, Pageidae; 5, Kokomopteridae; 6, Rhenopteridae; 7, Laurieipteridae.

tial characters for the separation of families in the other non-stylonuroid eurypterids. Størmer was the first to apply this criterion for separation of the Rhenopteridae from the Stylonuridae—a step that is correct, progressive and a definite contribution to a better taxonomy.

With this thought in mind, it becomes obvious that the family Stylonuridae needs radical revision on a world-wide basis, necessitating the description of new families and genera. In general, therefore, I shall use the structure of the prosomal ventral shield and the shape of the metastoma as criteria for the separation of families. Genera are based on the shape of the carapace, shape and position of the eyes, the type of opisthosoma and the size, shape and count of the podomeres. Unfortunately, for some unknown reason the opercula of the Stylonuracea are little known, and knowledge of these in the future will be of considerable importance toward a better classification.