Traditionally, P. rectidens and P. incertus have been recognized as two valid species; Western European workers recognized P. rectidens while Russian workers recognized P. incertus. Both Josifov (1986a) and Derzhansky (2000) treated these two species as synonyms (Josifov used rectidens as senior synonym, Derzhansky used incertus). Josifov (1986a) was the first revisor, and he selected P. rectidens.
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