There are several published cladistic studies on fossil gastropods.  As might be expcted, it depends on the characters as to how useful they are.  Vermeij, Dan Miller, and Peter Wagner come to mind as some authors to check.  Formal cladistic analyses on the Bivalvia are much fewer; the Evolutionary Biology of the Bivalvia volume just published by the Geological Society of London has one based almost entirely on shell data, with quite a few characters.

    Dr. David Campbell
    "Old Seashells"
    Biology Department
    Saint Mary's College of Maryland
    18952 E. Fisher Road
    St. Mary's City, MD  20686-3001 USA
    [log in to unmask], 301 862-0372 Fax: 301 862-0996
"Mollusks murmured 'Morning!'.  And salmon chanted 'Evening!'."-Frank Muir, Oh My Word!