Measurements were taken to the nearest millimeter by means of a millimeter stick. Body length is the distance from the tip of the snout to the posterior edge of the anal plate; tail length, from the latter point to the tip of the tail; and total length, the sum of the body plus tail. Descriptions of color are based on preserved specimens. Where descriptions of the color of living individuals are given, the data were taken from Kodachrome slides made available to me by William E. Duellman. Due to the transient nature of the longitudinal dark stripes in these snakes, no standard terminology has been devised, except that the posterior continuations of the stripes which on the head pass through the eye are termed lateral stripes; the posterior continuations of the median stripe of the head are termed dorsolateral stripes. A paravertebral stripe is one that is present on the scale-row on either side of, but not including, the mid-dorsal (vertebral) scale-row. In order to reduce confusion in the discussion of variation, the numbers designating the rows of dorsal scales are written as 1st, 2nd, whereas the numbers designating the stripes are written as first, second. Except in three dried skeletons, teeth were counted on dentigerous bones _in situ_. Since teeth are often missing, the sockets were counted in order to obtain an accurate count. In accounts of the species and subspecies, the observed range of variation is followed by the mean in parentheses; in some instances the mean is followed by the standard deviation, also in parentheses. An example is 65-79 (70.6 ± 3.93). Each synonymy includes all generic and specific combinations known to me that have been used for the genus, and, in addition, references to catalogues, checklists, and reports of collections. Localities of occurrence that are not plotted on the distribution maps are recorded in italic type under Specimens Examined. In the list of Specimens Examined the localities and specimens are listed in the following order: countries in alphabetical order; states or departments in alphabetical order in each country; localities in alphabetical order in each state or department; museum numbers in numerical order after the abbreviations of names of museums. When more than one specimen bears a single catalogue number, the number of specimens is given in parentheses following the museum catalogue number. Specimens for which data are given only as to country or to state or department are listed first after the name of that political unit under "no specific locality." The abbreviations for the museum collections are: