The laws in St. Louis City proper are pretty tight. There are no venomous allow, no crocs, and no snakes over 8ft (it might be 12ft). There are no permits available either. I believe the fine if you get caught is fairly hefty as well.
In St. Louis county, anything is allowed with an inspection, permit, and state registration. HOWEVER> Many many many municipalities have their own set of laws that rule over the coounty laws. For example, if you want to own a hot snake, you cannot do it in Kirkwood, Webster Groves, Clayton, Crestwood, Brentwood, etc etc etc.