These are Brachiopod shells which, according to the University of Kentucky, probably are the most commonly collected fossil in Kentucky. Brachiopods were (and are) marine species. They have an extensive fossil record, first appearing in rocks dating back to the early part of the Cambrian Period, about 525 million years ago. Most Brachiopods became extinct at the end of the Permian Period, about 250 million years ago. More than 90 percent of all living species are believed to have gone extinct during this time. Some Brachiopod species live in the world's oceans today.I have found the marine fossils of brachiopods, crinoids and coral in abundance along both along Harrods Fork Creek and Crocus Creek. - Wendy Butler Burt