Oh cool - from the picture it looks like a species of olive shell. They are great sand stirrers and the shells are some of the most beautiful of all the snails. They are always shinny when they are healthy and growing. I've picked them up when I was diving and kept them in my reefs. Very enjoyable. Some can get to be 3 and maybe nearly 4 inches long from what I recall of them. No doubt some are small, others maybe larger. Maybe this will help you find it on that link above?