The type species of the genus Biddulphia was first described under the name Conferva biddulphianum and included three species but no generitype. Boyer transferred C. biddulphianum to Biddulphia and B. biddulphiana was designated its generitype. Because of evolving taxonomic concepts, the taxonomy of Biddulphia is somewhat chaotic, with hundreds of published species and varieties in need of critical re-examination but numerous workers have limited the genus to include only those species with valves having pseudocelli. Taxonomic keys to Biddulphia allocated species to three groups: species with valves having folds, e.g. B. tuomey; species with transverse ribs, e.g. B. biddulphiana; and species without additional transverse structures, e.g. B. mobiliensis, which was recently transferred to Trieres. The Cretaceous, Paleogene and Neogene sediments of the former Soviet Union contain abundant fossil diatom assemblages and species of Biddulphia. Re-examination of B. heteromorpha with the scanning electron microscope