The only shells you are likely to get by trapping methods are those gastropod
species which are scavengers, that is, which commonly feed on dead flesh.
Conus and Oliva are not likely - they feed primarily on live prey.  Strombus
would be even less likely - they are vegetarians.  Some Murex species can
definitely be trapped though, as can members of the families Buccinidae,
Melongenidae, Nassariidae, Fasciolariidae, and sometimes Naticidae.  Of
course, hermit crabs will be attracted to bait, so you may get other kinds of
shells that way.
Paul M.