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Mellita quinquiesperforata
Since you found this specimen in SC, then it is more likely M. isometra. Mellita quinquiesperforata is a tropical species...
Your sand dollar still has the gray hairy surface that live sand dollars have. The white ones are old dead ones that have lost their "skin".
Good. I was going to help you look for a species ID but I see that someone has already answered for you. Does his identification match what you saw?
Kristin,
Do you think you know what this may be called? Even if you don't know the species, can you think of a common name for this creature?