perigonium

from The Century Dictionary.

• noun In Hydroida, a sac formed by the more external parts of the gonophore.
• noun In botany, same as perigone.

from the GNU version of the Collaborative International Dictionary of English.

• noun Same as perigone.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The sterile parts of a flower; collectively, the sepals and petals (or tepals); the perianth.
• noun The modified leaves around the antheridia in a bryophytic plant.
• noun dated The wall of the sporosac in a hydroid.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun collective term for the outer parts of a flower consisting of the calyx and corolla and enclosing the stamens and pistils