The Devonian psammosteid agnathan Psammosteus livonicus Obruchev is revised using analysis of fossil material from collections in Russia, Latvia, Lithuania and Estonia that allowed the diagnosis and description of this species to be substantially extended. P. livonicus is similar to other species of Psammosteus in the characters of the dorsal plate, cyclomorial tesserae and stenobasal shape of the branchial plates. The study of morphology of the branchial plates and tesserae (genus-level features) with consideration of species-level features of the ornamentation proves that establishment of the genus Oredezhosteus Moloshnikov is baseless. The species Psammolepis aerata Obruchev in Halstead Tarlo 1965 and Oredezhosteus kuleshovi Moloshnikov 2009 are included as junior synonyms into the revised species based on the ornamentation features.