The taxonomic status of some Ephemeroptera species is still not finally established. Such a situation is found in the case of a few species from the family Baetidae. Procloeon nana and Pseudocentroptiloides shadini have been included in the past in one of the following genera: Centroptilum, Cloeon, Procloeon or Pseudocentroptiloides. The changes in the taxonomic positions of these species are presented, starting from their first descriptions. After critical analysis of all these opinions, the following status: Procloeon nana (Bogoescu, 1951) and Pseudocentroptiloides shadini (Kazlauskas, 1964) is considered valid. On the basis of the material from the river Bug (North-West Poland), the different stadia: nymph, male and female imagoes, egg are redescribed and the main diagnostic features are presented.