Revision of Pleurodictyum lonsdalii Rh. Richter, 1855, a representative of the genus Petridictyum Schindewolf, 1959 (Anthozoa, Tabulata, Lower Devonian, Thuringia)

The original material of Pleurodictyum lonsdalii Rh. Richter, 1855, preserved in natural cast, has been traced (10 syntypes) and studied in detail as well as an additional 52 specimens from the same area and horizon (topotypes) collected by Yolk and Zagora. A lectotype is designated and the species lonsdalii definitively assigned to the genus Petridictyum Schindewolf, 1959. Petridictyum lonsdalii, mainly characterised by wide round tipped interseptal furrows and narrow septal ridges, differs from all other Petridictyum and is interpreted as a perhaps endemic taxon of the Early Upper Emsian - Nowakia cancellata Zone - of the western Thuringian Slate Mountains (Saxothuringian Terrane, North Gondwana).