David Campbell wrote, "True, although the extinction rate for lower and mid-Pliocene species in the eastern U.S. is exceptionally high. In this particular case, those researchers I know of who have looked at it agree that there are enough differences (rib number, size, inflation) to warrant separation. These do not include the individual to whom you alluded, although with his exceptionally low standard for recognizing new species, he would doubtless agree that the two are distinct." Indeed. And other people are free to knock these species down to subspecies rank if they think it is warranted. Most biostratigraphers applaud the subdivision of lineages into species or subspecies, since it makes their job of distinguishing the ages of strata easier. Though, when I see a paper that claims that a single bed yields six closely related species that no one else can tell apart, I raise an eyebrow. It does happen, of course, e.g., with species of modern Cerithium; but usually it's a sign of oversplitting. It makes work for the next researcher, by forcing him or her to measure the length, height, etc. of hundreds of shells just to prove that they all belong to one variable species. All that, just to return the taxonomy to where it had been before the splitter did his work. Andrew K. Rindsberg Geological Survey of Alabama