American Horsemussel
Modiolus americanus (Leach, 1815)
This shell has now been positively IDed bu Harry Lee as an American Horsemussel. It's known also as the Tulip Mussel. The shell is rare on S. Hutchinson Island beaches and I've found 10 of them.
A good condition specimen (February 2021)
Rough condition American Horsemussels (S. Hutchinson Island, December 2020)