hese 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.

Most large collections of garter snakes contain misidentified
specimens. The diagnostic differences in color and pattern are often
obscured, especially if the specimens are poorly preserved. Many
specimens deviate from the scalation typical of the form they
represent, and key out to other species. Isolated records should
therefore be accepted with caution. A case in point is Colorado
University Museum No. 46, from Buford, Rio Blanco County, Colorado,
originally identified by Cockerell (1910:131) as _Thamnophis sirtalis
parietalis_. This specimen, and another, now lost, from Meeker in the
same county seemingly served as the basis for mapping the range of
_sirtalis_ across the western half of Colorado, for there seem to
be no other records from this part of the state. However, a
re-examination of the specimen from Buford shows it to be an atypical
individual of another species, _T. elegans vagrans_. A specimen of
_T. radix haydeni_ (Col. U. Mus. No. 3165) was the basis for Maslin's
(1959:53) record of _parietalis_ in Baca County on the north fork
of the Cimarron River in southeastern Colorado. Brown (1950:203) has
mentioned the difficulty of defining the range of _sirtalis_ in the
southern Great Plains because of misidentifications of the similar _T.
radix_.

The range of the common garter snake has never been adequately mapped
in the Rocky Mountain and Great Basin states. Recent general works
(Smith, 1956:291; Wright and Wright 1957:834; Stebbins 1954:505;
Conant 1958:328) which have shown maps of the over-all range of
_sirtalis_, d