ROUND, F.E., & H. HÅKANSSON 1992 ("May") [postmarked Aug. 14] Cyclotelloid species from a diatomite in the Harz mountains, Germany, including Pliocaenicus gen. nov. Diatom Res. 7(1): 109-125, 53 figs. [including comparisons among Cyclotella, Cyclostephanos, Stephanodiscus, and Pliocaenicus]