What does "pallial" mean?

Pallial: Of or pretaining 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 (Zoöl.), the cavity inclosed by the mantle. -- Pallial sinus (Zoöl.), an inward bending of the pallial line, near the posterior end of certain bivalve shells, to receive the siphon. See Illust. of Bivalve.