Collected this in Plano, Texas when I was a kid back in the early 1980s.  Construction equipment had dug up some limestone and piled it next to the road.  There were a lot of broken Inoceramus shells, this was the only intact fossil that I found.  Looks different than Inoceramus.  Does anyone know what species this would be.  I have never found another like it.  Measures 2 3/8 inches across.