My dear "O.S."
    St Mary's College? When did the move take place? Do they have a better football team than NC?  Inquiring minds want to know.
            Art

bivalve wrote:

> A close reading of Andy's post might give a hint as to why Moore was not helpful.  The oysters are in their own part of the Treatise on Invertebrate Paleontology, as that section was not ready when the two volumes on the rest of the Bivalvia were published.
>
> Exogyra, like all true oysters, is pleurothetic on the left valve.  Almost all oysters start out attached to something with the left valve, but some species of Exogyra are among the few that seem to have managed to adapt an unattached lifestyle.  It is rather distinctive and easily reworked, so it could easily be washed downstream out of its normal range.  Exogyra is one of the commonest genera in the type Waccamaw section, which is uppermost Pliocene to perhaps earliest Pleistocene.  The Exogyra are reworked from underlying Peedee deposits.
>
> As Andy noted, they are gryphaeids, more closely related to Hyotissa, Neopycnodonte, and assorted extinct forms than to the standard Ostrea, Crassostrea, Lopha, etc.  Although Abbott only lists Hyotissa as reaching Florida, I have a valve collected deep off North Carolina.  The evolutionary relationships of the two groups have been debated, but molecular data (mostly unpublished so far) supports a close relationship between the gryphaeid and ostreid oysters.  The foamy internal texture mentioned by Andy is a very good indicator of the gryphaeid group.  Often examining the margin of the shell under low magnification (hand lens to low microscope) will reveal broken or worn edges displaying this.  It may be visible to the eye in thick-shelled specimens.  Pycnodonte has especially been commonly overlooked in faunas by assuming that it is just another Ostrea.
>
> The gryphaeids had substantial extinction at the end of the Cretaceous, with Exogyra and related forms disappearing.
>
>     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!