Sexual dimorphism is evident in all species and subspecies of _Conophis_. Differences always exist in the number of subcaudals and in the tail/body ratio; males have more subcaudals and relatively longer tails than do females (table 3). Otherwise, there is little sexual dimorphism in these snakes. Males and females cannot be differentiated by any feature of coloration. Formulation of a biological concept of the species as defined by Mayr (1942) is difficult when most of the data primarily relied upon are from preserved specimens. Nevertheless, a total view of variation was attempted so that differences within and between populations could be recognized. Differences, between populations, that seem to be part of a continuous or internal cline (Huxley, 1942) are not used for characterizing subspecies. [Illustration: FIG. 1. Patterns of dorsal coloration at mid-body of adults of all species and subspecies of the genus _Conophis_ except _C. lineatus concolor_. A. _C. lineatus dunni_ (UMMZ 107339) from Santa Rosa, Guatemala. B. _C. lineatus dunni_ (UMMZ 116537) from 1.5 mi. N Matagalpa, Nicaragua. C. _C. lineatus dunni_ (ANSP 3480) from "San Jose," Costa Rica. D. _C. l. lineatus_ (KU 23253) from Río Blanco, 20 km. WNW Piedras Negras, Veracruz, México. E. _C. nevermanni_ (ANSP 22424) "San Jose," Costa Rica. F. _C. pulcher_ (UIMNH 33646) from Soconusco, Chiapas, México. G. _C. vittatus_ (KU 39626) from Atencingo, Puebla, México. H. _C. vittatus_ (TCWC 9473) from 1 mi. S Colotlipa, Guerrero, México. I. _C. vittatus_ (UMMZ 82653) from "vicinity of" Salina Cruz, Oaxaca, México. Approximately × 3/4.] =Conophis lineatus= (Duméril, Bibron and Duméril) _Tomodon lineatum_ (in part) Duméril, Bibron and Duméril, Érpétologie Genérale, 7(pt. 2):936-938, February 25, 1854. _Diagnosis._--No dark pigmentation posterior to nape; lateral dark stripe anteriorly passing through eye and posteriorly involving 4th or 3rd and 4th scale-rows only; first scale-row darkly pigmented; no paravertebral dark stripe; six to thirteen (or no) dark stripes at mid-body; usually eight (sometimes seven) supralabials immaculate white or having dark ventral margins.