The species _pulcher_ probably differentiated from the remaining _lineatus_ stock during the Early Pleistocene orogenic upheaval in Guatemala. The _pulcher_ stock was isolated on the Pacific Coastal slopes of Guatemala, while _lineatus_ moved through the subhumid corridor of northern Middle America into México and southward toward Costa Rica (Stuart, 1954a). In the Late Pleistocene and Recent, _pulcher_ moved back across the central Guatemalan highlands occupying its present range in northern Middle America. Primarily because of the formation of unsuitable habitat (wet forest) that presently separates the geographic ranges of populations of _lineatus_, this species differentiated into three subspecies. SUMMARY The genus _Conophis_ Peters, 1860, contains four species. Three are monotypic and the fourth has three subspecies, making a total of six taxa. The genus is characterized by maxillary teeth of equal size followed by a diastema and two enlarged grooved fangs. The scales are smooth, in 19 rows at mid-body, and 17 nearer the tail. The anal is divided, apical pits are lacking, the head shields are normal for a colubrid, and the hemipenis is bilobed having many large basal spines. The six taxa are separated primarily on the basis of color pattern, but characters of scutellation, including numbers of dorsals, ventrals, caudals, and places of reduction of the number of dorsal scale-rows, were analyzed. Snakes of this genus are distributed throughout semi-arid environments from southern México southward into Costa Rica. They feed upon lizards, primarily of the genus _Cnemidophorus_; in addition they are known to eat small rodents and other snakes. _Conophis_ is a member of the subfamily Xenodontinae and, as presently understood, has no known living close relatives. A single specimen of _Dryinoides_ from the Miocene of Montana has been compared with this genus. The genus _Conophis_ is thought to have evolved in Middle America. The present distribution and differentiation probably are primarily the result of climatic fluctuations in Middle America, which produced the areas of subhumid environment where _Conophis_ presently lives. LITERATURE CITED AUFFENBERG, W. 1958. A new genus of colubrid snake from the Upper Miocene of North America. Amer. Mus. Novitates, 1874:1-16. February 27. COPE, E. D. 1861. Contributions to the ophiology of Lower California, México and Central America. Proc. Acad. Nat. Sci. Philadelphia, 13:292-306. December 28. 1867. Fifth contribution to the herpetology of tropical America. Proc. Acad. Nat. Sci. Philadelphia, 18:317-323. February 20. 1871. Ninth contribution to the herpetology of tropical America. Proc. Acad. Nat. Sci. Philadelphia, 23(2):200-224. October 24. 1876. On the batrachia and reptilia of Costa Rica. Journ. Acad. Nat. Sci. Philadelphia, series 2, 8(4):93-154, 6 pls.