The Collaborative International Dictionary of English v.0.48:

Peritreme \Per"i*treme\, n. [Pref. peri- + Gr. ? a hole.]
   (Zool.)
   (a) That part of the integument of an insect which surrounds
       the spiracles.
   (b) The edge of the aperture of a univalve shell.
       [1913 Webster]