Hi, I found this external mold shell on Honeymoon beach, Florida USA. It's about 2" long and 3/4" on the widest end. Unfortunately it is broken and worn on the right edge, but I still thought it was a cool find. It's limestone and has about 3 more shell imprints on the flip side (not shown). This was an unusual shape so I made a clay mold to better see the shape (3rd photo)I looked through many seashell books and narrowed it down to Eastern Turritella or Florida Cerith. What do you think?