>    Doesn't "fossil" indicate that the material makeup is replaced by some other mineral? If so, wouldn't a sub-fossil be a long-dead critter to which that process had not begun---or proceeded very far?<

Not necessarily; there are shells about 300 million years old that still have original aragonite, and original calcite is known back to about 450 million; some of these may also have traces of the organic components as well.  However, these do show some alteration from the original.  On the other hand, some fossils have no mineral at all and are just impressions where the original shell dissolved away.  Only a few years in a poorly-buffered stream can be enough for a unionid shell to dissolve away.  Some modification in the mineralogy can also take place quickly, depending on the chemistry of the environment.

>    NOTE: I hope you tell the proper authorities at Alabama that you can still kick extra points.<

Naming a species for Bear Bryant might help funding around here.  In fact, the collections building is named for Mrs. Bryant.  However, fans of fossil mollusks may be more familiar with the namesakes of Tuomey Hall and Smith Hall.

    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