This is a fossil scallop shell (likely Nodipecten sp.) that was recovered from a Miocene-era (approx. 5 to 23 million years ago) deposit in Florida's famous Bone Valley Formation. It is an internal cast that shows some detail and has nice size at 5-inches in diameter.
Refer to the photos. The black centimeter cube is shown for scale and is not included. You are purchasing the specimen shown. Your purchase will include an ID label.