Abstract

"The Mediterranean Ermoceras Douville and the boreal Arkelloceras Frebold, both of Bajocian age, are not related to the Stephanoceratidae as previously assumed but are derived from either the hammatoceratid Abbasites Buckman or its direct descendants, the Otoitidae. The descent of both the Thamboceratidae, as hitherto understood, and of the Clydoniceratidae from Ermoceras is confirmed, although both families may have evolved parallel rather than successively. In this genus are also placed three Arabian species hitherto referred to Stephanoceras and Teloceras, including 'S.' arabicum Arkell. Ermoceras was indeed the first thamboceratid and is therefore placed in the Thamboceratidae. Arkelloceras is provisionally included in the same family."

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