The large genus _Coluber_ is much in need of revision. Its many
species, perhaps more than a score in all, occur in North America from
southern Canada south to Guatemala, in eastern and southwestern Asia,
in southern Europe, and in North Africa. All are active,
slender-bodied snakes having smooth scales in few rows, and having
large eyes with well developed vision. The North American species fall
into two natural groups, the typical racers, and the whip snakes,
often assigned to a separate genus, _Masticophis_ (Ortenburger, 1928).
The whip snakes are more specialized than the typical racers in having
the eyes more enlarged, and the body form more slender and attenuate,
with number of scale rows more reduced. The racers of the Old World
are more diverse. Inger and Clark (1943) suggested a partitioning of
the genus _Coluber_ on the basis of the pattern by which scale rows
are reduced, from the maximum number on the forebody to the minimum
number at the posterior end of the body, supplemented by certain
characters of the hemipenis and of the cephalic scutellation. Besides
_Coluber_ and _Masticophis_ these authors recognized within the group
the genus _Platyceps_ with several species in southern Europe and
southwestern Asia; _Zamenis_ with several species in the same region
and in North Africa, and _Haemorrhois_, a monotypic genus of Spain,
North Africa and several Mediterranean islands. Although apparently
valid in principle, this arrangement has not been generally followed.
Exclusive of those species groups whose assignment to the genus
_Coluber_ are somewhat questionable, the remaining species in the
genus are: _C. constrictor_ occurring throughout most of the United
States and south along a narrow Atlantic coastal strip of Mexico to
Guatemala; _C. oaxacae_ of southern Mexico; and _C. spinalis_ of
northern China. _C. oaxacae_ is poorly known as only a few specimens
have been collected, but seemingly it is a near relative and
derivative of _C. constrictor_, especially of that species'
southernmost population. _C. spinalis_ is much more distinct, as might
be expected from its geographical remoteness. It is a slender, active
snake, of olive coloration dorsally with 17 scale rows and a bright
yellow, black-edged dorsal stripe and yellow ventral surface. It is
relatively small (up to 755 millimeters snout-vent length) and is
partial to riparian habitats but is also found in forests and in dry
and barren regions (Pope, 1935:224-226). It is known to feed upon
lizards.