Siphonal and cameral deposits inAllumettoceras and the position of the tripteroceratidae (nautiloidea)

Abstract

New material here assigned to the Tripteroceratidae (Orthoceridae, Nautiloidea) contain cameral and siphonal deposits. Cameral and siphonal deposits are believed to have become suppressed in most later lineages of the family, producing the taxonomically ambiguous morphology seen inTripteroceras and many species ofAllumettoceras. The Tripteroceratidae are considered to have been derived from a pseudorthoceratid stock present in the Baltic and/or western or peri-Gondwana during the Llanvirn Series. The family had expanded into North America and beyond by the Caradoc Series. This expansion in distribution may be associated with theNemagraptus gracilis transgression.