Southwest at a time when cooler and moister climate prevailed. Other fossil occurrences are of late Pleistocene age--Vero Beach and Seminole, Florida (Brattstrom, 1953a:245) and, doubtfully, Rancho LaBrea, California (Brattstrom, 1953b:376). The range of _mormon_ has been mapped (Wright and Wright, 1949:134) as extending east to south-central Montana on the basis of one specimen allocated on the basis of two characters. Otherwise the range of _mormon_ seems to be entirely west of the Continental Divide, well separated from that of _flaviventris_ by desert and mountain barriers. The conspecificity of _mormon_ with the other subspecies needs to be more thoroughly investigated, and geographic variation within _mormon_ also merits study. Geographic Variation The common racer and the several species of whip snakes (_Masticophis_) were revised by Ortenburger (1928). More recently with much larger series of specimens, Auffenberg (1955) again revised the classification of _C. constrictor_, but his study was concentrated in Florida and neighboring southeastern states with relatively little attention devoted to populations of the western and central United States. As the species occurs throughout most of the United States and south through the coastal lowlands of eastern Mexico to Guatemala, it is found over a wide range of environmental conditions. Various characters are subject to geographic variation, and some of them follow clines that are maintained over extensive areas. Such characters as the number of hemipenial spines, and the enlargement of one or more basal spines into hooks, the shape of the premaxillary bone, the number of maxillary teeth, the numbers of ventrals and caudals, color of eye, number of dorsal saddle-marks and of ventral spots in juveniles, and ratios of body proportions including tail length to total length have been used to characterize the subspecies. Also important is the shade of coloration of adults. The subspecies _constrictor_, _priapus_ and _helvigularis_ that are characteristic of forested habitats in the eastern United States are black dorsally and have their ventral surfaces suffused to a large extent with dark or dusky coloring. Farther westward the ground color becomes progressively paler, greenish, grayish or light brown, and the ventral surface is yellow (white on the throat and neck). The same tendency appears in _C. c. paludicola_ of the Everglades. The populations of arid climates in southern Texas and in the far western states are relatively pale colored. The species thus conforms to Gloger's Rule in changing from a pallid coloration in arid climates to a dark pattern with eumelanins predominating in a humid climate.