Source : Webster's Revised Unabridged Dictionary (1913)

Perigonium \Per`i*go"ni*um\, n.; pl. {Perigonia}. [NL.]
   Same as {Perigone}.

Source : WordNet®

perigonium
     n : collective term for the outer parts of a flower consisting
         of the calyx and corolla and enclosing the stamens and
         pistils [syn: {perianth}, {chlamys}, {floral envelope}, {perigone}]
     [also: {perigonia} (pl)]