The study is fo cused on the tax o nomic in ven tory of an in trigu ing bi valve fauna from the Lower Oligocene Menilite Beds (Dynów Marls) within the Silesian Nappe, Pol ish Outer Carpathians. Six teen bi valve spe cies have been iden ti fied within the ma te rial col lected in two small quar ries in Jabłonica Polska near Krosno. Strati graphic and geo graphic dis tri bu tions of all recog nized spe cies are con sid ered. This as sem blage, the first of this kind in Po land and one of three rec og nized in the Outer Carpathians, shows clear af fin i ties to co eval typ i cal Solenovian fau nas from Ukraine to Kazakhstan, with par tic u lar com par ison made to bi valve fau nas from the Menilite For ma tion (Subchert Mem ber) within the Boryslav-Pokuttya Nappe, Ukrai nian Outer Carpathians. More over, this study pres ents an over view of the main as pects and def i ni tions of the date of the Paratethys or i gin. The main cri te rion used to de fine the time of the Paratethys birth is the dis tinct fau nal turn over from the mod er ately di verse bo real or Tethyan bi valve fau nas pop u lat ing par tic u lar bas ins of the North ern Peri-Tethys in the ear li est Oligocene to the uni form, highly en demic fauna in hab it ing the newly formed semi-closed ba sin. This vast in land sea, named Paratethys, was pop u lated by rep re sen ta tives of eight euryhaline bi valve fam i lies. They are char ac ter ized by ex tinct Paratethyan gen era, such as Bessia Kojumdgieva et Sapungieva, Merklinicardium Popov, Korobkoviella Merklin, Urbnisia Goncharova, Ergenica G. Popov and Janschinella Merklin.