_T. s. parietalis_ differs from _fitchi_ in several trenchant characters, and there are additional slight or average differences between the two. In approximate order of their importance the differences are as follows: 1) The red (or pale yellow or green or buffy) marks on skin between the scales on the upper half of the dorsolateral area (that is between the sixth and seventh, seventh and eighth and eighth and ninth scale rows) present in _parietalis_ are missing in _fitchi_ or are represented by only an occasional small fleck. 2) The dorsolateral area is black or nearly so in _fitchi_ but averages paler in _parietalis_, in which a wide range of shades may be found from black to olive brown. 3) The red of the dorsolateral area frequently invades the lateral stripe, which sometimes is mostly red, and may even invade the ventrals in _parietalis_, but in _fitchi_ the red marks are usually confined to the dorsolateral area, and do not invade the lateral stripe. 4) The prominent paired black dots or semicircular marks on the anterior edge of each ventral in _parietalis_ are largely lacking in _fitchi_, which rarely has any dark marks on the ventral surface. 5) The dorsal stripe consistently involves the middorsal scale row and the adjacent half of the next row on each side, and is bright yellow in _fitchi_, but in _parietalis_ it may be slightly wider, may be duller with more dusky suffusion, and its edges may be less sharply defined. INTERMEDIATE AND ATYPICAL POPULATIONS Of many specimens examined from eastern Oregon, Idaho, Utah, Wyoming and Colorado, few were typical of either _parietalis_ or _fitchi_. Many were intermediate in some respects or showed a composite of characters of the two subspecies. No well-defined belt of intergradation exists, but the transition extends over more than a thousand miles, with local populations somewhat isolated and slightly differentiated along divergent lines. In view of this situation some plausibility could be claimed for any of several dividing lines between the subspecies. However, by far the most logical division is the Continental Divide; south of the Teton Range it constitutes a broad barrier separating eastern and western populations. Across Montana and Canada also it constitutes a more or less formidable barrier, with high altitudes and cold climates that probably are limiting to garter snakes. With few exceptions the snakes from east of the Continental Divide are more nearly like _parietalis_ in the sum of their characters whereas those from west of the Divide are more nearly like _fitchi_.