Two new Upper Bathonian species: Progonocythere polonica n. sp. and Progonocythere ogrodzieniecensis n. sp. are described from the Clydoniceras discus zone in Ogrodzieniec near Zawiercie, Poland. The ontogeny and development
of the hinge in the successive instars of the species P. polonica n. sp. have been studied. The presence there has been ascertained of a sieve plate closing up the lumen of straight pore canals.