IONS

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_.

In the Teton Range and in Yellowstone National Park these garter
snakes occur in headwater streams up to the Continental Divide.
KU 27956 from Two Ocean Lake 3-1/2 miles northeast of Moran, Teton
County, Wyoming, agrees in its characters with _fitchi_, having the
red lateral marks small and inconspicuous, discernible only on the
anterior half of the body. The dorsolateral area is dark, almost
black. The ventrals lack dark markings.

In Utah, populations of _sirtalis_ occur in the drainages of the Bear,
Weber and Sevier rivers and other smaller streams of the western
half of the state. Obviously the species invaded Utah from the north,
probably at a time when Lake Bonneville, the predecessor of the
present Great Salt Lake, drained into the Snake River of Idaho.
Van Denburgh and Slevin (1918:190) separated from their western
"_concinnus_" and "_infernalis_" and allocated to _parietalis_ the
populations of Utah and southeastern Idaho, but presumably these
authors were not familiar with typical _parietalis_ of the Mid-west.
Subsequent authors (Wright and Wright, 1957:834; Stebbins, 1954:505;
Conant, 1958:328) have followed this arrangement. A re-examination of
specimens from Utah, including living individuals collected at Bear
Lake in the summer of 1959, indicates that they should be assigned to
_fitchi_ rather than to _parietalis_.

Likewise va