>  I was under the opinion that chomata is restricted to the subfamily
>  PYCNODONTEINAE, family GRYPHAEIDAE.

Chomata occur throughout the Ostreoidea, both in Gryphaeidae and in Ostreidae.  They are distinctive and prominent in most pycnodontines but occur in Ostrea edulis and many other true ostreids.  See, e.g., Stenzel in the Treatise on Invertebrate Paleontology.

    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

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