In Atlantic Coast Line R. Co. v. Florida, 295 U.S. 301, 55 S.Ct. 713, 79 L.Ed. 1451 (1935), although the Court denied restitution to the party who paid, pursuant to an order later held invalid, freight rates in excess of the last valid rates, the Court's analysis rested on the view that restitutionary power was "ancillary" to the power of the district court to determine the validity of the Commission's order. Id. at 314.