The taxonomic affinities between the extinct acmaeid Collisella edmitchelli (Lipps. 1966) and Recent California species has been previously studied using highly variable exterior shell characters. I use shell structure, a character I believe to be more conservative than either shell or radular morphology, to determine the taxonomic and phylogenetic relationships of this species. The shell structure of C. edmitchelli is identical to that of C. scabra (Gould. 1846). This shell structure group is not known to occur in any other acmaeid species. Although closely related to C. scabra, C. edmitchelli is morphologically distinct and is retained as a valid, extinct species known only from Late Pleistocene deposits on San Nicolas Island. California.