Cymbasoma sinopense sp. nov. is described from an adult female collected off the Sinop coast, in the southern Black Sea, Turkey. This is the first species of this genus recorded from the Black Sea coast of Turkey. The new species is a member of the widespread Cymbasoma longispinosum species-group, and it closely resembles C. chelemense Suarez-Morales & Escamilla, 1997 from the Yucatan Peninsula and C. califonziense Suarez-Morales & Palomares-Garcia, 1999 from the Gulf of California. This species can be distinguished by a combination of subtle characters, including the body proportions, the structure and armature of the fifth legs, the ornamentation of the genital somite, and the relative length of the ovigerous spines. A previous report of C. longispinosum from the northern Black Sea probably represented a misidentified record of C. sinopense sp. nov. The Mediterranean reports refer to a species that is different from the one of the Black Sea. Comparative comments and data including the main taxonomic characters of members of the Cymbasoma longispinosum species-group are presented. Overall, it is confirmed that records of this species from different geographic areas should be revised carefully because they could represent undescribed species. A key for the identification of the females of the currently known species assigned to the Cymbasoma longispinosum species-group is included.