Recently found materials of large beyrichiacean ostracodes from the Early Devonian of the Darlik, Korucukoy, and Kabalakdere sections in NW Anatolia stimulated the restudy of ostracode collections from the Istanbul area, including the Toula collection (GBA Vienna) and Endriss collection (previously in GPI Marburg and currently in SMF Frankfurt), and their biostratigraphical and palaeogeographical significance. The species Gibba kayseri, Gibba schmidti, Zygobeyrichia roemeri, Zygobeyrichia subcylindrica, and Zygobeyrichia onusta are documented and beyrichiid gen. et sp. indet. is described. There are great similarities with ostracode faunas from Early Devonian shallow-water sediments of Europe and North Africa (in Germany from the Rhenish Schiefergebirge to Thuringia, northern France, Spain, Poland, Bohemia, Podolia, Moravia, and North-West Africa). Therefore, this distribution questions the presence of a deeper and wider Rheic Ocean, which would be difficult for shallow-water benthic organisms to cross.