Abstract: In literature about the mandible dentation of IJo/yergus l'1!lescells incorrect formulations in the sense of "reduced" have .become common. lndeed the denticles have characteristics which should be seen as autapomorphics and play an essential role in piercing the enemy caput to destroy the central nervous system. In contraI)' the ,'ltrulIgylognathus which it is often compared to, is toothless but for a preapical denticle. It doesn't pierce the caput like P. rujescells as assumed in textbooks but penetrates with it's mandible through the mouth to the brain. The much strained convergence of both taxa is put into question.