This bivalve is 10mm long and from the Lower Cretaceous of Cooke County Texas. It's probably from the Duck Creek Formation but may be from the Ft. Worth Formation. It may even be the Goodland. I'm sure I've seen them other places but I just now brought one home and need to give it a proper label. These formations would be of Albian Stage or Washita Group in Texas. It looks a little like some Ostrea sp. I've seen in some references but not exactly the same. Any help would be great.