New records of psammosteids (Heterostraci) from the Aruküla Regional Stage (Middle Devonian) of the Leningrad Region, Russia

Previously unknown exoskeletal plates of certain Middle Devonian psammosteids, i.e., Pycnosteus palaeformis Preobrazhensky, Psammolepis proia Mark-Kurik, and Schizosteus (?) sp., from localities of the Aruküla Regional Stage of the eastern part of the Main Devonian Field (Leningrad Region, Russia) are described. The psammosteid Schizosteus (?) sp. described in open nomenclature in connection with the absence of well-preserved median plates has only been found in several localities (Zaitsevo, Siverskii, and Belogorka). The shape of the branchial plate of Tartuosteus giganteus (Gross) and ventral plate of Psammolepis proia is specified. The psammosteid Psammolepis proia from the eastern part of the Main Devonian Field is described for the first time.