A silica plate extending internally from the apical portion of the valve. To contrast, a pseudoseptum is part of a valve, while a septum is part of a copula, or girdle band. The pseudoseptum occurs in some species of Gomphonema, Gomphoneis, Stauroneis, and Navicula. Plural form is pseudosepta.
Round, F.E., Crawford, R.M. and Mann, D.G. (1990). The Diatoms. Biology and Morphology of the Genera. Cambridge University Press, Cambridge, 747 pp.