We just got back from our vacation in Aruba and my son found a strange shell near Eagle Beach where the sand stops and the rocks begin. We love to explore that area. Normally we have noticed these shells embedded in the rock and figured they were very old. Then this trip he found one in perfect condition laying on the ground. It is about 3 inches in length and slightly curved. It looks like a giant rolly polly bug shell, if that helps you get an image. It is greyish brown with distinct lined sections that are slightly raised.