It is accepted male genitalia are not diagnostic, but spermathecae are partly diagnostic within the genus Cassida Linnaeus, 1758 (Coleoptera: Chrysomelidae: Cassidinae). However, studies on genitalia have been based only on stereomicroscopic examination. The ultrastructure of genitalia has mostly not been studied. The aim of this study was to determine whether this ultrastructures could be diagnostic. Aedeagi and spermathecae of 63 specimens of Cassida viridis Linnaeus, 1758 were collected from Qankiri, Hatay, Kayseri, Osmaniye and Zonguldak Provinces in Turkey in 2003, 2007 and 2015, and examined for the first time. Thus, new diagnostic characters were obtained and it revealed that it was diagnostic to either species or subgenus. Photos of aedeagus and spermatheca taken with both SEM and stereomicroscope are given.