Abstract

A group of small annulate Pennsylvanian cyrtocones and orthocones is demonstrated to represent the immature deciduous portions of large smooth breviconic nautiloid cephalopods. The family Brachycycloceratidae is proposed to include several species of the single genus, Brachycycloceras. Some of the shell features of the family, especially the characteristic "siphuncular displacement canal," mark it as a homeomorph of the early Paleozoic Ascocerida.

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