Key to PA Crayfishes

4a    Dorsomesial 1/3 of palm of chela (the area of the chela's propodus below the movable finger (dactyl)) covered with tubercles and gape of chela slight (fig A); eyes are somewhat reduced and postorbital ridges without spine or tubercle (fig B) - Cambarus thomai (Found in southwestern PA.  A burrower, common in roadside ditches and clay banks of larger streams. Sometimes under stones in streams.)

4b    Dorsomesial 1/3 of palm of chela not covered with tubercles and gape of chela moderate to large (fig A); eyes not reduced and postorbital ridges ending in a spine or tubercle (fig B) - Cambarus diogenes (Common in western PA, and reported in southeastern PA.  A burrower, it is usually near spring-fed swamps around the drier edge, or near steams in logged areas, and is typically found in lower elevations.  Can tolerate turbid water.)