The Everglades crayfish (Procambarus alleni Faxon) is the only species reported from Everglades National Park (ENP) and Big Cypress National Preserve (BICY). However, we identified a second species, Procambarus fallax (Hagen), from those locations. Reexamination of archived samples showed that P. fallax had been collected as early as 1985 but had been misidentified or overlooked; therefore, we provide methods for distinguishing live and preserved specimens of these morphologically similar species. Species relative abundance varied predictably with hydroperiod (length of inundation) both in recent collections and in archived samples. Procambarus fallax relative abundance was highest in sites characterized by long hydroperiod and prolonged inundation, whereas P. alleni was the lone species in short hydroperiod marshes.