V. N.  Zlatarski, Paleobiologichni Izsledvaniya Vrkhu Madrepori ot Urgona v Sredniya Predbalkan [Paleobiological Aspects of Madreporian Corals from the Urgonian in the Middle Predbalkan]. Sofia: Blgarska Akademiya na naukite Geologicheski Institut, 1968, p. 28.