Involucra

from The Collaborative International Dictionary of English v.0.48

Involucrum \In`vo*lu"crum\, n.; pl. L. {Involucra}, E.
   {Involucrums}. [L. See {Involucre}.]
   [1913 Webster]
   1. (Bot.) See {Involucre}.
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   2. (Zool.) A sheath which surrounds the base of the lasso
      cells in the {Siphonophora}.
      [1913 Webster]