Calyptra n. : A little hood or veil, resembling an extinguisher in form and position, covering each of the small flasklike capsules which contain the spores of mosses; also, any similar covering body.

Example:
What is the difference between a Calyptra and an operculum?

Taxonomy
Calyptra, free encyclopedia, genus, tissue, Botany, Articles lacking sources, bryophytes, archegonia, capsule, Flowering plant, Stamen, search, Unsourced, moss, Tortula muralis, moth, venter, maturity.

Defination from the web:
calyptra is an enlarged archegonia venter that protects the capsule. This cap is lost at maturity. In flowering plants, the calyptra is a covering tissue for stamens and carpels. The name is also used for the capping tissue of roots. This botany article is a stub. ...