Oyster of some kind... hard to know where to look, as it could
be Paleozoic to Pleistocene. Probably Ostreidae... Andrew G.
It's an oyster; there's a good chance that it has been called
"Lopha" but there are gryphaeid and ostreids, not to mention
several different genera in each family, that can look somewhat
like that. The oldest oysters are Triassic. If he can find out anything
about the local geology (try the California state geological survey),
that would greatly help in narrowing down the age.
Looking closely at the specimens with a hand lens, if broken surfaces
show a foam-like internal structure, it's a gryphaeid.-- Dr. David
- is Dendostrea? vespertina (Conrad) a Miocene to Pliocene fossil
from the Salton Trough of southern California....Chuck P.