I answered Chewieee's other thread. This snail is probably Pardalina testudinaria (called Pyrene testudinaria in most of the popular literature). If so, it's a columbellid, in the Dove Shell family. Gray Reefer's is definitely a columbellid, and is probably also Pardalina testudinaria, although it's apparently a different subspecies. (Some authors would consider the two to be separate species rather than subspecies.) I think both should be good guys in your tanks.
Cheers,
Don