An Ilymatogyra arietina pelecypod fossil found in Grayson Marl Formation of Tarrant County, Texas. Animals lived in the upper Cretaceous Period. Check out Dave's write up on this fossil on the Views of the Mahantango blog: CLICK HERE
Thanks to Mark for these fossils.
A smaller Ilymatogyra arietina pelecypod fossil is shown in the next three images.
