The Collaborative International Dictionary of English v.0.48:
Pallial \Pal"li*al\, a. [L. pallium a mantle. See Pall.]
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.
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.