Guide to Stephanodiscus niagarae

Valves are concentrically undulate, so that only the valve margin or the valve center is in focus at one time. The areolae are round and arranged in fascicles of radial striae, separated by raised costae. Areolae are 11-20 in 10 µm. Striae are uniseriate in the center valve and biseriate near the margin. Marginal spines are present. Marginal fultoportulae are present, positioned below the spines. Central fultoportulae are also present in the valve center, singly or in a ring. One or more rimoportulae are present near a marginal spine, with a spine-like external extension.