Spermathecae of the type species of six subgenera in the genus CassidaLinnaeus, 1758 have been studied and figured. Spermathecal structures of these species on the base of 24 specified characters were evaluated in detail under both stereo microscope and Scanning Electron Microscope (SEM). It is demonstrated that the characteristics of the spermathecal structure obtained particularly with SEM studies can be used at almost all taxonomic level diagnostically. It is obvious that the characteristics, however, will have different values for different taxonomic categories. As a result of this study, in spermathecae, vasculum, ampulla, ductus glandula auxiliaris and ductus spermatheca are generally constant in shape within species, but distinctive and useful in comparison with other species. As an important output of the study, it is observed that the type species and therefore the subgenera can be divided chiefly into 3 diverse group based on spermathecal structures: C. seraphina in C. (Alledoya) and C. nebusa in C. (s. str.) as Group I; C. nobilis in C. (Cassidulella) as Group II; C. viridis in C. (Odontionycha), C. brevis in C. (Onychocassis) and C. murrea in C. (Pseudocassida) as Group III. The new grouping is discussed previous groupings based on host plants and stereo microscopic abservations due to lack of available SEM studies. Eventually, the spermathecal structure of the species examined in this study was found to be distinctive not only at the subgenus level but also at the species level. According to the ultrastructure of spermatheca, it was revealed that the genus CassidaLinnaeus, 1758 is a polyphyletic group, not monophyletic. In addition, the key to the diagnosis, which is formed according to the general characters and external and spermatecal morphological features of adults of the studied species, is given.