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Webster 1913 Edition

Noun.

[Gr. [GREEK] a covering, lid, fr. [GREEK] to block up.]

(Zoöl.)

A membranaceous or calcareous septum with which some mollusks close the aperture of the shell during the time of hibernation, or estivation.

epiphragm ‎(plural epiphragms)

A dry layer of mucus used by a snail or mollusk to seal itself inside its shell during hibernation.