The species of genus Plourdosteus are single representatives of family Coccosteidae in the Upper Devonian of the East European Platform. Three species, P. livonicus, P. mironovi and P. trautscholdi, were found in the Franian deposits of the Main Devonian Field. P. timanicus was known from the South Timan. A more precise diagnosis of genus Plourdosteus is made. The new material on P. timanicus is studied and compared with the diagnosis on Plourdosteus. It is a new independent genus close to the genera Eastmanosteus, Golshanichthys and Ulrichosteus by the morphology of skull roof. The arthrodires are referred to take up an intermediate position between the families Coccosteidae and Dinichthyidae and, probably, need to be singled out into an independent family. -English summary