Late response, but there are several Potamotrygon species not mentioned.
The Atlantic stingray is best kept in marine or brackish, unless you can verify that the specimen came from St. John's River in Florida.
There are a number of Asian and Australian freshwater rays, including Fluvitrygon species, however, these are very rare.
There are also a number of South American species from genera similar to Potamotrygon that are technically legal in your state.