Rhodoliths from the Middle Miocene (Badenian) deposits of the Korytnica Basin are analysed in terms of environment-related internal features (symmetry, massiveness, growth forms of algae, borings, algal species composition and distribution). Differences in internal structure and distribution of dominant species in the rhodolith populations from Korytnica and Chomentów reflect environmental differences between the two parts of the Korytnica basin. Dense, symmetrical rhodoliths built frequently of thin thalli, with frequent epibionts and rare borings are typical of the shallower part of the basin (Chomentów). Porous, asymmetrical rhodoliths, built mainly of thick thalli, with less frequent epibionts and common borings prevail in the deeper part of the basin (Korytnica). In the systematic part of the paper 26 species of 7 genera (Archaeolithothamnium, Wlaeothamnium, Lithothamnion, Mesophyllum, Lithophyllum, Leptolithophyllum and Titanoderma) are described, 7 of which are for the first time reported from the Polish Miocene.

Key words: rhodoliths, red algae, paleoecology, systematics, Miocene, Poland