English: Skull diagram of Helicoprion davisii, based on specimen IMNH 37899 as described and illustrated by Tapanila et al. (2013) and Ramsay et al. (2014/15). The chondrocranium/neurocranium is not preserved in the fossil. It has been reconstructed based on preserved material from Caseodus, Ornithoprion, Fadenia, Edestus, and other autodiastylic holocephalans, as well as artwork published in Tapanila et al. (2013) by Ray Troll. In life, the majority of the tooth whorl would have been protected by an "encasing cartilage" (sensu Ramsay et al. (2014/15)); the encasing cartilage is not shown here, in order to better illustrate the structure of the tooth whorl.