roactive application. Usery v. Turner Elkhorn Mining Co., 428 U.S. I, 17, 96 S.Ct. 2882, 2893, 49 L.Ed.2d 752 (1976). FN19. Article I contains two Ex Post Facto Clauses, one directed to Congress (§ 9, cl. 3), the other to the States (§ 10, cl. 1). We have construed the Clauses as applicable only to penal legislatio