The Cenomanian ammonites of the Helvetic Domain (French-Swiss Western Alps) are revised and illustrated for the first time since the middle of the 19th century. The faunas occur in remarkable condensed hemipelagic glauconite-rich biomicrites that also contain planktic foraminifera and small stromatolites. Thirty-three ammonite species referred to 15 genera are described; the assemblage extends from the lower part of the Lower Cenomanian Mantelliceras mantelli Zone (Neostlingoceras carcitanense Subzone) to the lower part of the Middle Cenomanian Acanthoceras rhotomagense Zone (Turrilites costatus Subzone). The assemblage comprises 57% trachyostracous forms, 41% heteromorphs of the standard NW European sequence, and 2% leiostracous forms, which inhabited an external shelf biome. The biogeographic affinity of this fauna is essentially cosmopolitan (69%), but 31% of the specimens belong to the European Boreal biota, with no Tethyan taxa. -Authors
