FIGURES 50–55 in Morphology of some fossil lacustrine centric species from the western United States assigned to the genus Cyclotella (Bacillariophyta), including four described as new

FIGURES 50–55: Cyclotella stoermeri. SEM. Figures 50–52. External valve views. Fascicles are comprised of 1–3 rows of small areolae. The ribs are thickened and elevated, becoming thinner on the valve mantle. The valve center has enlarged areolae. Scale bars = 10 and 3 µm, respectively. Figures 53–55, internal valve views. Complex and simple alveolae are positioned around the perimeter of the valves. Thick and thin costae are evident, and marginal fultoportulae are evident on the recessed costae. Rimportulae are positioned also on the recessed costae. Areolae with domed cribra are evident in the center of the valves. Scale bars = 3, 2 and 1 µm, respectively.