B, Similar plant with an almost mature sporogonium; s, seta; f, capsule; c, calyptra.
"Encyclopaedia Britannica, 11th Edition, Volume 4, Part 3" by Various
Calyptra: a hood or cap; see alula.
"Explanation of Terms Used in Entomology" by John. B. Smith
Calyptra, applied to the portion of volva covering the pileus.
"The Mushroom, Edible and Otherwise" by M. E. Hard
Calyptra turnip-shaped, abruptly globose above.
"The Manual of the Botany of the Northern United States" by Asa Gray