The expression of intergradation between _guadalupensis_ and _pallidus_ is of a clinal nature that involves parallel changes in the pattern on the snout, side of head, limbs (to a lesser degree), tuberculation along the anterior edge of the carapace, size of whitish tubercles or dots, and the distinctness of the blackish ocelli that surround the whitish dots on the carapace. These characters form a well-marked gradation or cline that extends over a considerable area. There is, however, no continuous environmental gradient because the populations are relatively isolated by occupying adjacent drainage systems. The sharpest break in the gradation of characters mentioned above occurs between the Colorado River and Brazos River drainages. The population of softshells in the Colorado River drainage is actually an intergradient one, but more closely resembles _guadalupensis_, whereas the population in the Brazos River drainage more closely resembles _pallidus_. For convenience the turtles inhabiting the Colorado River drainage are referred to _guadalupensis_ and those in the Brazos River drainage to _pallidus_. Some individuals from farther west than the Colorado River drainage will resemble _pallidus_, and a few individuals from father east than the Brazos River drainage will resemble _guadalupensis_. The gradation of some of the characters mentioned above terminates in the subspecies _emoryi_. It, however, has characters not found in _pallidus_ or _guadalupensis_, and is more distinct from either of those subspecies than either is from each other; the difference in characters as well as the break in the gradient of characters between _guadalupensis_ in the Nueces River drainage and _emoryi_ in the Río Grande drainage is greater than that between _guadalupensis_ in the Colorado and _pallidus_ in the Brazos River drainages. I have refrained from designating individuals between these three subspecies (_emoryi_, _guadalupensis_ and _pallidus_) as "intergrades" on the distribution maps, and only mention (in text) those individuals whose characters show a decided tendency toward the adjacent subspecies. For further comments on intergradation see the account of _T. s. pallidus_.