ississippi River and the
Rocky Mountains is almost as large. The more western _T. s. fitchi_
occurring from the Oregon and California coasts east through the
northern Great Basin, has the third largest range, while the far
western subspecies _pickeringi_, _concinnus_, _infernalis_ and
_tetrataenia_, and the Texan _T. s. annectens_ all have relatively
small ranges.

Since the publication of Ruthven's revision of the genus _Thamnophis_
more than 50 years ago, little attention has been devoted to the study
of this widespread and variable species, except in the Pacific Coast
states (Van Denburgh, 1918; Fitch, 1941; Fox, 1951). However, Brown
(1950) described the new subspecies _annectens_ in eastern Texas,
and many local studies have helped to clarify the distribution of the
species in the eastern part of the continent and to define the zone of
intergradation between the subspecies _sirtalis_ and _parietalis_. In
our study attention has been focused upon _parietalis_ in an
attempt to determine its western limits and its relationships to the
subspecies that replace it farther west.

TAXONOMIC HISTORY

_Thamnophis sirtalis parietalis_ Say was described (as _Coluber
parietalis_) in 1823 from a specimen obtained in what is now
Washington County, Nebraska, on the west side of the Missouri River
three miles upstream from the mouth of Boyer's River [Iowa], or
approximately eight miles north of Omaha. Although the type locality
was unequivocally stated in the original description, Nebraska was not
mentioned since the state was not yet in existence. Because the mouth
of Boyer's River, the landmark by means of which the type locality is
defined, is in Iowa, the impression has been imparted that the type
locality itself is in Iowa (Schmidt, 1953:175), and to our knowledge
the type locality has never been associated with Nebraska in the
literature.

Like all the more western subspecies, _parietalis_ is strikingly
different from typical _sirtalis_ in having conspicuous red markings.
The relationship between the two was early recognized. Several of
the other subspecies were originally described as distinct species.
_Coluber infernalis_ Blainville, 1835; _Tropidonotus concinnus_
Hallowell, 1852; _Eutainia pickeringi_ Baird and Girard, 1853; and
others now considered synonyms eventually came to be recognized
as conspecific with _Thamnophis sirtalis_. Ruthven (1908:166-173)
allocated all western _sirtalis_ to either _parietalis_ or