PROTASPIDES OF UPPER CAMBRIAN APHELASPIS (PTYCHOPARIIDA, TRILOBITA) AND RELATED SPECIES WITH THEIR TAXONOMIC IMPLICATIONS.

The ontogeny of Aphelaspis brachyphasis is illustrated and described on the basis of newly discovered silicified material from the McGill section, Nevada, USA. Protaspides of three other Aphelaspis species are redescribed. Of ptychopariide species for which protaspides have been documented, the protaspides of those previously considered to be closely related to Aphelaspis are illustrated herein. Protaspides of Aphelaspis are most similar to those of Olenus, supporting previous taxonomic suggestions that the Aphelaspidinae is closely related to the Olenidae and may be assigned to the Olenacea. The protaspides of Housia share few similarities with those of Aphelaspis, contradicting the hypothesis that these genera are placed together within the Pterocephaliidae. [ABSTRACT FROM AUTHOR]