Source : Webster's Revised Unabridged Dictionary (1913)

Peristome \Per"i*stome\, n. [Pref. peri- + Gr. ?, ?, mouth.]
   1. (Bot.) The fringe of teeth around the orifice of the
      capsule of mosses. It consists of 4, 8, 16, 32, or 64
      teeth, and may be either single or double.

   2. (Zo["o]l.)
      (a) The lip, or edge of the aperture, of a spiral shell.
      (b) The membrane surrounding the mouth of an invertebrate
          animal.

Source : WordNet®

peristome
     n 1: (botany) fringe of toothlike appendages surrounding the
          mouth of a moss capsule
     2: region around the mouth in various invertebrates