The siliceous two-valved shell of a diatom, with its contents.

A spore formed in diatoms by the union of two cells or by the excessive growth of an individual cell. Also, the resting-spore of the diatoms.

Botany. Applied to the overlapping edge of one of the valves of the frustule of the Diatomaceæ; called also the ‘girdle’.

Botany. One of a number of internal projections occurring in the valves of diatomaceous plants.

The silicified crust or shell of a diatom: more usually called frustule, n.