The Collaborative International Dictionary of English v.0.48:

Pallial \Pal"li*al\, a. [L. pallium a mantle. See Pall.]
   (Zool.)
   Of or pertaining to a mantle, especially to the mantle of
   mollusks; produced by the mantle; as, the pallial line, or
   impression, which marks the attachment of the mantle on the
   inner surface of a bivalve shell. See Illust. of Bivalve.
   [1913 Webster]

   Pallial chamber (Zool.), the cavity inclosed by the mantle.


   Pallial sinus (Zool.), an inward bending of the pallial
      line, near the posterior end of certain bivalve shells, to
      receive the siphon. See Illust. of Bivalve.
      [1913 Webster]