Ontogenetic variation in PL/HW, mean PL/HW of specimens having plastral lengths 7.0 centimeters or less, 4.09, and exceeding 7.0 centimeters, 5.50; ontogenetic variation in CL/CW, mean CL/CW of specimens having plastral lengths 8.5 centimeters or less, 1.12, and exceeding 8.5 centimeters, 1.21; mean CL/PCW, 2.02; mean HW/SL, 1.30 (including subspecies _hartwegi_); mean CL/PL, 1.39.
_Variation._--Variant individuals include: UMMZ 72512, an adult male, having some ocelli seven millimeters in diameter that are almost solid spots; UMMZ 89659 having postocular and postlabial stripes connected on right side of head; UMMZ 95615, 52948, 54402 having inner dark borders of pale stripes on snout represented by short dashes and dots (a ragged line connecting anterior margins of orbits on 54402); UMMZ 52948, 89659 having interrupted, black marginal lines on carapace with ends of some segments oriented inward and overlapping portion of adjacent segments; UMMZ 81699, female having plastral length of 19.0 centimeters, lacking conspicuous tubercles on anterior edge of carapace; UI 2403, CNHM 92204 having extensive dark mottling and marbling on throat and neck, undersurface of limbs and posterior portion of carapace.
_Comparisons._--_T. s. spinifer_ can be distinguished from all other subspecies of _T. spinifer_ by the presence of large black ocelli (diameter 9-10 mm. on adult males, 2-3 mm. on hatchlings) in combination with only one dark marginal line. _T. s. spinifer_ resembles _asper_ in having ocelli or dots on the carapace but differs from _asper_ in having only one dark marginal line and larger ocelli. _T. s. spinifer_ differs from _hartwegi_ only in the large size of the ocelli. _T. s. spinifer_ resembles _hartwegi_ and _asper_ but differs from _pallidus_, _guadalupensis_ and _emoryi_ in having blackish spots and ocelli on the carapace and lacking whitish dots. _T. s. spinifer_ resembles _hartwegi_, _asper_, and _pallidus_ and differs from _guadalupensis_ and _emoryi_ in having conical or knoblike tubercles on the anterior edge of the carapace on large females.
_T. s. spinifer_ differs from the subspecies _asper_, _guadalupensis_ and _emoryi_ in having a relatively narrower head, and from _emoryi_ in having a relatively wider carapace. _T. s. spinifer_ resembles _hartwegi_ and _asper_ but differs from the other subspecies in having the carapace widest at a plane approximately one-half way back on the carapace. The subspecies _spinifer_ and _hartwegi_ have longer snouts than _pallidus_, _guadalupensis_, and _emoryi_. _T. s. spinifer_ differs from _asper_ but resembles all the other subspecies in having a relatively longer plastron.