This contribution constitutes a taxonomic and systematic revision of the lacustrine gastropod fauna of the locality Džepi in the Prozor Basin (Bosnia and Herzegovina). 15 gastropod species were detected in the course of the present study, belonging to the families Neritidae, Melanopsidae, Hydrobiidae, Pachychilidae and Planorbidae. The fauna revealed a high degree of endemism (66.6%) and low biogeographic relationships to coeval middle Miocene faunas of the Dinaride Lake System (DLS; maximum of

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... shared species 14.3%). None of the species has been documented from outside the DLS. The generic composition with abundant melanopsids and hydrobiids but rare pulmonates is typical among DLS faunas and characteristic of shallow long-lived lakes. Since a large part of the type material of former investigations is lost, we designate five neotypes to settle the taxonomic status of the respective species. In addition, five lectotypes are defined from existing syntype series. Based on the occurrence of the biostratigraphical marker species Illyricocongeria cf. aletici (Brusina, 1907) (Bivalvia: Dreissenidae) and faunal similarities to the Kupres Basin the deposits are classified into the early Langhian (ca 15.3-15.0 Ma). Illyricella gen. nov. and Illyricella dzepiensis gen. nov. sp. nov. (Truncatelloidea: Hydrobiidae) are introduced as new, endemic taxa. •