_Comparisons._--_T. s. guadalupensis_ can be distinguished from all other subspecies of _T. spinifer_ in having: (1) large white dots, sometimes three millimeters in diameter, on a dark background usually surrounded with blackish ocelli and conspicuous on the anterior half of the carapace (some as large as those on posterior half) in adult males, and (2) whitish dots on the anterior half of the carapace, in hatchlings, that are often encircled with dark ocelli. _T. s. guadalupensis_ resembles _pallidus_ and _emoryi_ in having white tubercles or dots on the carapace and therein differs from _spinifer_, _hartwegi_ and _asper_. _T. s. guadalupensis_ resembles _pallidus_ but differs from _emoryi_ in having a pale rim that is less than four times wider posteriorly than laterally. _T. s. guadalupensis_ resembles _emoryi_ but differs from _pallidus_, _spinifer_, _hartwegi_ and _asper_ in having along the anterior edge of the carapace tubercles that are flattened or wartlike prominences often lacking sharp tips in adult males; these tubercles are never conical in large females. _T. s. guadalupensis_ has a wide head, a feature shared with the subspecies _asper_ and _emoryi_, but differs from _emoryi_ in having a wider carapace. _T. s. guadalupensis_ resembles _emoryi_ and _pallidus_ but differs from the other subspecies in having the carapace widest farther posterior than one-half the length of the carapace. The length of snout in _pallidus_ and _guadalupensis_ is shorter than in _spinifer_ and _hartwegi_ but is longer than in _emoryi_. _T. s. guadalupensis_ differs from _asper_ but resembles the other subspecies in having a relatively long plastron. _Remarks._--Some individuals of _guadalupensis_ have characteristics that are applicable to _emoryi_. TNHC 12352 (Llano River) a hatchling, has conspicuous white dots confined to the posterior third of the carapace; the pale rim, however, is not widened posteriorly. TU 10156 (Guadalupe River) has a conspicuously widened pale rim on the carapace that is approximately 3.4 times wider posteriorly (8.5 mm.) than laterally (2.5 mm.). _T. s. guadalupensis_ more closely resembles _pallidus_ than _emoryi_. Turtles living in rivers that drain into the Gulf of Mexico east of the Guadalupe-San Antonio river system successively show increasing resemblance to _pallidus_ from west to east.