Found in northern SC. Believed to be a Carolina Heel Splitter. I would like to know more about what I found. Seems to have been injured at a young age. Terminology would also be helpful. If these pictures don't show enough I can upload more.
This is a type of blister on the shell, most likely caused by a parasite that bored its way through the outside of the shell. It wouldn't be considered a blister pearl, unless it was durable/beautiful enough to be cut out and used as jewelry. Click on the link to see another example on an abalone shell - I think you'll really like it!