The siliceous parts of the diatom cell wall. Composed of the larger
and the smaller
The epitheca overlaps the hypotheca similar to a pill box or Petri dish. From Latin for a little piece.
See also valve and cingulum.
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.