Not that some of the northeastern states don't have some idiot laws, but why would dead oyster shells be illegal. In Maryland they're used to cover driveways and the last time I checked, chicken farmers feed crushed oyster shells to chickens for egg production.
Why is it illegal to be in possession of a raptor feather? Because they don't know where you got it from. It is illegal in IN to have a native mussel shell. Well-meaning but ill-thought out rules.