These changes left most of the populations formerly included in _concinnus_ and _infernalis_ without a name, and Fitch (_op. cit._) revived _Thamnophis sirtalis tetrataenia_ (Cope) to apply to them. However, Fox (1951:257) demonstrated that the type of _T. s. tetrataenia_ came from the San Francisco peninsula (rather than from "Pit River, California" as erroneously stated in the original description) and that the name was applicable to a localized peninsular population rather than to the wide-ranging far western subspecies, which he named _T. s. fitchi_. The range of _fitchi_ includes California west of the Colorado and Mohave deserts (except for the narrow strip of coast occupied by _infernalis_ and _tetrataenia_), Oregon except the northwestern part, Washington east of the Cascade Range, most of British Columbia, extreme southeastern Alaska (occurring farther north than any other terrestrial reptile of North America) and parts of Idaho. Neither Fox (1951) nor Fitch (1941) defined the eastern limits of _fitchi_ or discussed its relationship to the subspecies _parietalis_. Wright and Wright (1957:849) stated: "Fitch ... did not even mention the big scrap basket form _parietalis_, from which he pulled _T. s. fitchi_ (old _tetrataenia_). That comparison remains to be made, and the east boundary of _fitchi_ and the west boundary of _parietalis_ are still nebulous." We have undertaken to define better than has been done before the ranges of _parietalis_ and _fitchi_ and to list the diagnostic characters separating these two subspecies. Freshly collected material of both has been compared. At the time of his 1941 revision the senior author had never seen a live or recently preserved specimen of _parietalis_. DISCONTINUITY OF RANGE Wherever it occurs at all, the common garter snake is usually abundant. Because of its diurnal habits and the concentration of its populations along watercourses, it is not likely to be overlooked. There are few, if any, remaining large areas in the United States where herpetologists have not carried on field work. It may be anticipated that certain rare and secretive species will still be found far from any known stations of occurrence, and seeming gaps in the ranges of these species will eventually be filled. But for the common garter snake the negative evidence provided by the lack of records from extensive areas should be taken into account in mapping the range.