Linda, Harry, Trish and others,

Thank you so much for the information on Agripoma!

Agripoma texasianum is discussed in the following article, which has been
posted on the Web:
Cruz-Abrego, F. M., and Flores-Andolais, Felipe, 1991, Distribucion de
moluscos y caracterizacion ambiental en zonas de descarga de aguas
continentales del Golfo de Mexico (Mollusks' distribution and environmental
characterization in the river plumes of the Gulf of Mexico): Anales del
Instituto de Ciencias del Mar y Limnologia, v. 18.
http://biblioweb.dgsca.unam.mx/cienciasdelmar/instituto/1991-2/articulo394.h
tml

Adding this to your information, it seems clear that Agripoma is not at all
uncommon in the Gulf in U.S. and Mexican waters, just restricted to muddy
areas near the mouths of rivers. Broken and whole Agripoma valves occur in
many shell samples collected from Dauphin Island (Alabama) beaches in 2003
and 2004, well before Hurricane Ivan. The seafloor south of Dauphin Island
is eroded during storms, and muddy currents from Mobile Bay make the water
quite turbid in contrast with the beautifully clear water off Gulf Shores
(Alabama) and Pensacola (Florida), not very far to the east. Presumably,
between storms, mud is deposited offshore and Agripoma thrives. During
storms, the shells are washed onshore, where they persist for a while before
being broken up.

Harry mentioned Bob Parker. I never met him, but in the 60's he conducted an
important series of studies on the distribution of mollusks with regard to
their sedimentary environments in the Gulf of Mexico and Gulf of California.
The research was funded by the American Association of Petroleum Geologists,
which recognized that mollusks can be used to deduce the depositional
environment of ancient rocks, and thus indirectly to locate petroleum.
Mollusks are not used much for this purpose anymore, since smaller fossils
(foraminifera, ostracodes, coccoliths) tend to be more abundant and less
damaged in well cuttings. But mollusks are still useful in contexts where
such microfossils are absent.

All the best,
Andy

Andrew K. Rindsberg
Geological Survey of Alabama

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