Abstract
Fallacia cassubiae sp. nov. is described from extant and subfossil sediments of Puck Bay (southern Baltic Sea). The new taxon possesses features typical of the diatom genus Fallacia Stickle et Mann, and is characterized by an indistinct lyra structure, expanded central area and the extent of the canopeum is limited to the lyra structure and some short finger-like extensions of the canopeum. Some ecological requirements of F. cassubiae are given.