The frustule is really a box, composed of an upper and lower lid, each fitted with a girdle band around the edge (N. Ingram Hendey).
Useful english dictionary. 2012.
frus — frus·to·conical; frus·tra·ne·ous; frus·trat·er; frus·trat·ing·ly; frus·tra·tion; frus·tra·tive; frus·tu·la·tion; frus·tule; frus·tu·lum; frus·tum; frus·trate; frus·trum; … English syllables
frustule — frus·tule … English syllables
frustule — frus•tule [[t]ˈfrʌs tʃul[/t]] n. mcr the shell of a diatom • Etymology: 1855–60; < F < LL … From formal English to slang
Frustule — Frus tule, n. [L. frustulum, dim. fr. frustum a piece: cf. F. frustule.] (Bot.) The siliceous shell of a diatom. It is composed of two valves, one overlapping the other, like a pill box and its cover. [1913 Webster] … The Collaborative International Dictionary of English
