Dr. Sue Kidwell has done a lot of work on the similarities between dead and live assemblages; for details on this sort of thing, try searching for her name in paleontological journals.

Certainly there are a lot of ways for stray specimens to turn up.  I have seen crabbed Babylonia from Tampa Bay and Cerion in Bahamas seagrass flats, and Hugh Porter has a story about someone discovering all sorts of exotic shells on the beach after her shell collection (and beach house) was wiped out by a hurricane.  Somewhat older material (e.g., Pleistocene) might not be easy to distinguish from modern at first glance.  For example, a survey for potential fisheries off South Carolina turned up a bed of dead Placopecten magellanicus, well south of the modern range.  Evidently they hit a bed from a glacial interval, but did not realize it.

Regarding GUTtata, collection ex pisces is resposible for the name Voluta indigesta.  Evidently the fish appeared to be having difficulty digesting it.

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL  35487-0345 USA
    [log in to unmask]

That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa