The large shells of some species of tridacna would be found vertically imbedded in the solid rock, in the position in which they lived.
"Coral-Reefs"
Darwin, Charles
10. tridacna 7 Indian and Pacific Oceans, Chinese Seas.
"Sea-Weeds, Shells and Fossils"
Peter Gray B. B. Woodward
A tridacna spread its jaws before his steps so that he nearly plunged into the deadly springtrap of the deep.
"Where the Pavement Ends"
John Russell