A new placenticeratid ammonite from the Albian (Lower Cretaoeous) of California and the inferred history of some placenticeratid and engonoceratid ammonites

A new ammonite species from the lower Cretaceous (middle Albian) of Califor nia is questionably assigned to Placenticeras MEEK, 1876 by its suture line whose lobe frillings are more regularly arranged than in most Placenticera s and by its ornamentation and coiling that resemble some Placenticeras. Th e California material shows strong similarities to Sokolovites CASEY, 1966, a member of the Gastroplitinae WRIGHT, 1952, and therefore suggests a hopl itid origin for the Placenticeratidae. A review of criteria separating the families Placenticeratidae HYATT, 1900 and Engonoceratidae HYATT, 1900 sugg ests possible relations between these families.