Article: Ammonites of the genus Acanthoceras from the Cenomanian of Rouen, France

Although Acanthoceras only forms a minority of the ammoniteifrom the Craie de Rouen, the locality is important as being the type locality of Acanthoceras rhotomagense, the type species of the genus and the most oft-quoted species. This study shows that almost all the Acanthoceras from Rouen can be regarded as one variable species which can be conveniently divided into five varieties, only one of which, A. rhotomagense var. clava-tum, is new. A. rhotomagense is a widespread species and marks an horizon low in the Middle Cenomanian. Acanthoceras basseae sp. nov., also from Rouen, is a rarity.