Exogyra aquila is thought to be the oldest exogyra oyster and is found in the Cow Creek and Hensell formations in Central Texas. Exogyra quitmanensis is a very similar fossil of the same age found in the Quitman formation of West Texas. Upon examining the literature I found it quite difficult to see any differences between these two species. The E. quitmanensis are thought to be larger and have greater convexity. Upon examination of the fossils from the Cow Creek formation in the University of Texas Geological repository I found that all specimens were identified as E. quitmanensis, although this was never published, to my knowledge. To address the question of the differences between the two species I have collected data from as many sources in the literature as I could find and using specimens collected by myself and B. Yurke have made the following plots. One might conclude from the plots that these two species should really be joined into a single species. In that case, the name E. aquila should be reserved for the European species and E. quitmanensis for the Texas species. Final determination of this question should wait until additional specimens can be collected from the quitman formation.
