Krassilov, V. A., Afonin, S. A. and Naugolnykh, S. V. (1999) “Permotheca with in situ pollen grains from the Lower Permian of the Urals”, Journal of Palaeosciences, 48((1-3), pp. 19–25. doi: 10.54991/jop.1999.1287.