Depressed Slippersnail

Depressed Slippersnail
Crepidula depressa Say, 1822
Family Calyptraeidae.

These are versions of the "flat" slippersnail. There are two very similar types the Depressed Slippersnail and the Black-foot Slipper Snail. This is probably the Depressed Slippersnail (H. Lee 2021).