A new species of crayfish, Cambarus (Lacunicambarus) erythrodactylus, is separated from the Cambarus (L.) diogenes complex. The new species is morphologically similar to C. (L.) diogenes but differs from it in the presence of three or four spines along the cervical groove, greatest depth anterior mid-horizontal beneath the antennal scale, the presence of two rows of tubercles along the distal medial palm, with an additional two or three partial or full rows of tubercles on the palm, subpalm of the chela with one to four (mode = three) tubercles, and a gonopod extending greater than 90° and bent cephalodistally 20° at the shoulder. The species occurs in the Pea, Choctawhatchee, Sepulga, and Conecuh River systems of southeastern Alabama, in the Black Warrior and Tombigbee River systems in western Alabama and eastern Mississippi, in the Alabama River in central Alabama, and Bear Creek drainage of the Tennessee River, and Yazoo River drainages and occurring throughout the central and eastern portions of Mississippi.