Elsewhere (1956:121) I have shown that males of _spinifer_ from Lake Texoma, Oklahoma, and scattered localities in Texas and Louisiana are sexually mature when they reach a plastral length of 9.0-10.0 centimeters. Adult males have distinct, convoluted, non-pigmented vasa deferentia and elongate testes, the maximal measurements of which are about 10 by 30 millimeters. Testes of hatchlings are approximately 4.0 by 0.4 millimeters (TU 13698.12, plastral length 3.2 cm., measured with ocular micrometer). I am not aware of seasonal changes in size of the testes. In reading the discussion that follows, it is well to remember that males having the cloaca extending beyond the posterior edge of the carapace are regarded as sexually mature. As an indication of geographic variation in _spinifer_, I have listed the measurements of the 10 smallest males for only those subspecies of which there are numerous records (Table 7). Corresponding data for _T. muticus muticus_ are also listed for comparison. TABLE 7. Size at Sexual Maturity of the 10 Smallest Males of T. m. muticus and Selected Subspecies of T. spinifer. The Extremes Precede the Mean (in Parentheses). ========================+======================= SPECIES AND SUBSPECIES | Plastral length (cm.) ------------------------+----------------------- _T. s. spinifer_ | 8.8-10.3 (9.6) _T. s. hartwegi_ | 9.6-10.5 (10.2) _T. s. pallidus_ | 9.1-11.2 (10.5) _T. s. guadalupensis_ | 9.3-10.8 (10.1) _T. s. emoryi_ | 8.2-9.0 (8.8) _T. m. muticus_ | 8.2-9.2 (8.7) ------------------------+----------------------- The data indicate that the size at which sexual maturity is attained in _emoryi_ (about 8.0-9.0 cm.) is less than in any other subspecies of _T. spinifer_ (about 9.0-10.0 cm.), and, more importantly, corresponds to that of _T. m. muticus_. Although the mean for _T. s. spinifer_ is slightly less than in the remaining subspecies, I doubt that there is any significant difference according to subspecies in the size at which sexual maturity is attained in the subspecies _spinifer_, _hartwegi_, _asper_, _pallidus_ and _guadalupensis_. The corresponding size in _T. m. muticus_ and _T. s. emoryi_ heightens the morphological resemblance between these forms. The only sexually mature male of _T. ater_, which morphologically resembles _emoryi_ and _muticus_, is 9.5 centimeters in plastral length. I do not know the size at which _T. ferox_ attains sexual maturity. The smallest sexually mature individual examined by me was 12.0 centimeters; probably _ferox_ attains sexual maturity at a larger size than _spinifer_ or _muticus_. The relative size of attainment of sexual maturity in _ferox_, _spinifer_, and _muticus_ corresponds to the maximum size of the three species; _ferox_ is the largest species and _muticus_ is the smallest (Table 2). _Size of Females at Sexual Maturity_