In the paper the authors describe Bythiospeum neglectissimum, a new species of Bythiospeum Bourguignat, 1882 found at a few stations in Southern Poland. It is characterised by its stout and Iow, conical and minute shell with the aperture closely adjoining and narrow, and by the slender, multifolded verge having a terminal dagger-shaped filament and medially an apparent lobe. The description comprises the shell, operculum, mantle, head, ctenidium, osphradium, radula, stomach, verge, and female reproductive organs. The species surpasses far the known ran­ge of the genus Bythiospeum, and its bionomy is completely unclear.