Olivia sayana
The Lettered Olive snail is named for the dark markings that vaguely resemble letters. They can be found by looking for the grooves it makes in the sand at low tide. Its specialty is burrowing rapidly, and is "the fastest shell in Florida" in this respect. It hunts bivalves and crustaceans, capturing them by its foot and taking them below the surface to consume.
Long ago Native Americans used these shells to make jewelry as do beach combers today. It is the state shell of South Carolina. The animal is large enough that it can extend its body out to cover the entire shell.
This gastropod lays 20 to 50 eggs which develop into larvae. These live in a planktonic form before they develop into adults.
Live shells should never be taken from any Florida State Park.