ABSTRACT The ranges of the 17 subgenera of the genus Procambarus, comprising 152 species and subspecies occurring in North America and Middle America, are illustrated and briefly outlined. A graphical compilation of the distribution of these crayfishes is presented showing that the greatest number of species and subspecies occur in the southeastern United States, with a decline in numbers centrifugally to Mexico where two centers of concentration occur on the eastern versant: one north and the other south of the Cordillera Volcanica Transversal. Evidence is presented for a postulated Procambarus track extending from the eastern part of the United States southwestward through Mexico, and thence northeastward to Cuba.