The Ontogeny of Certain Arietidan Oxycones

Abstract

The compressed angustumbilicate oxycones of the Deiran and Raasayan stages of the Lower Lias are generally assumed to be “homoeomorphous terminals of different lineages” of the Arietidae. But while the characters of the adult sutures of these forms link them with that family, there is comparatively little evidence as to the details of the ontogenetic developments of the various genera hitherto recognized. It is the purpose of this paper to repair this deficiency in some slight measure. The two forms selected, partially for convenience, are of considerably different ages: Victoriceras is a Raasayan form, while Oxynoticeras oxynotum occurs at a considerably lower horizon in the Deiran.