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Diatoms of the United States is now known as Diatoms of North America.
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Central nodule

A type of central process unique to the genus Orthoseira. The internal openings are simple, while the external openings are composed of well-defined collars.


Stoermer, E.F. and Julius, M.L. (2003). Centric Diatoms. In: Freshwater Algae of North America (J.D. Wehr and R.G. Sheath, eds) Elsevier Science pp. 559-594.