New record of Diplomoceras cylindraceum (Defrance, 1816) from the Maastrichtian of the Western Fore-Balkan (Bulgaria)

Abstract

New data on the heteromorph ammonite species Diplomoceras cylindraceum (Defrance, 1816) have been obtained from three localities of the Western Fore-Balkan (West Bulgaria). A retrospection of the earlier Bulgarian records is also presented. This characteristic species is relatively common in Bulgaria and, based on both previously and the newly collected data, it is confined to the Maastrichtian. Owing to the difficulty in collecting enough specimens, the amount of variation in ribbing and whorl-section shape, which have been used by other authors for determination of more species within Diplomoceras, is difficult to judge. Nevertheless, the Bulgarian material reveals that rib density varies in broad limits and the rib index does not show a sufficient degree of variance to warrant the distinction of more than one species. Therefore, it is doubtful that all specific names that have been proposed in the literature for rib differences represent other species than Diplomoceras cylindraceum.