Carcharodon megalodon from the Upper Miocene of Denmark, with comments on elasmobranch tooth enameloid: coronoïn

C. megalodon, not previously known from deposits in Denmark, is recorded from a large, but imperfect tooth derived from the marine clay exposed at the type locality for the Upper Miocene Gram Formation. Detached, large vertebral centra from this locality, probably belonging to the same species, are considered as well as the nomenclature and phylogenetic relationships of the genus and species. A revised list of the Gram clay elasmobranch assemblage is included. Elasmobranch tooth enameloid, now distinguished under the term coronorn and perfectly preserved in the C. megalodon tooth, is a mesodermally derived, hypermineralized hard substance. Its ultrastructural, histological and ontogenetic characteristics in elasmobranchs in general are touched upon and considered in comparison with similar features of other enameloids including acrodin of actinopterygians and varieties of pleromin occurring in dipnoan and chimaeroid dentitions. Corono1n and acrodin (both differing from pleromins in all essential features of ontogenetic formation and growth),, are characteristic of elasmo­branchs and actinopterygians, respectively, and these two groups separated phylogenetically far back in the Palaeozoic. It is not unexpected, therefore, that corono¥n and acrodin are found to be structurally distin­guishable from each other.