During studies of the benthic mircoflora of northern Lake Michigan, a small diatom was often seen which has been assigned to the genus Amphora by some researchers and to the genus Cymbella by others. The diatom was originally described as Amphora coffeiformis var. thumensis by Mayer in 1919. It has been reported as a rarely occurring member of fossil and recent floras from Europe and Asia since the 1930’s, and the generic position has often been discussed but not resolved. Cleve-Euler transferred the status of Mayer’s taxon to Amphora thumensis in 1932. In 1933, Krasske ignored the earlier name and called this same diatom Cymbella parvula. Hustedt, the most active and highly regarded modern ditomist, became convinced that this diatom should be placed within Cymbella, and most investigators follow his ideas today. All previous investigations have utilized only light microscopy.