Exogyra costata (Oyster)
Exogyra costata are commonly found in the Cretaceous strata in northeast Mississippi. This example from the Dunn-Seiler Museum shows damage to the growth lines that were repaired as the creature grew.
66 million years
Prairie Bluff Formation (Chalk)
Creative Commons Attribution Non-Commercial No Derivatives license
Moe-Hoffman, A. (collector), “Exogyra costata (Say 1871) showing damage to growth lines.,” Mississippi State University Libraries, accessed June 30, 2022, http://msstate-exhibits.libraryhost.com/items/show/1349.