Breckenridge (1955:6) wrote that the development of the mottled pattern "undoubtedly indicates a stage in the attainment of sexual maturity"; I have mentioned (1956:121) that the mottled pattern is apparent on females before sexual maturity is attained. To my knowledge females have no external characters which appear at the time of attainment of sexual maturity. Sexually mature individuals of _ferox_ have been described in various terms: 31-1/4 pounds (Goff and Goff, 1935:156); six pounds, lengths of carapace 10-1/2 and 13 inches (Hamilton, 1947:209); greatest width of head 3-1/2 inches (Wright and Funkhouser, 1915:120). A 10-1/2 inch carapace presumably represents the smallest turtle and corresponds to a plastron approximately 22.0 centimeters in length. There is no other information available concerning size at sexual maturity in _T. ferox_. There is little published information concerning the size at sexual maturity in _T. spinifer_. Cahn (1937:193) wrote that _spinifer_ in Illinois "must attain a carapace length of about 24 centimeters [plastral length approximately 18.0 cm.] before the females become sexually mature"; this statement is the basis for Smith's mentioning a length of 9-1/2 inches (1956:162). Evermann and Clark (1920:595) recorded the lengths of carapace of some females (presumably all adult) from Lake Maxinkuckee, Indiana, as 11, 11-3/4, 12-1/2, and 13 inches; the smallest measurement corresponds to a plastral length of approximately 21.0 centimeters. The data concerning reproduction presented in succeeding paragraphs is based principally upon examinations of turtles in the TU collections; I am indebted to Dr. Fred R. Cagle for permission to dissect these turtles. Females are regarded as sexually mature when they have oviducal eggs or corpora lutea or ovarian follicles exceeding 15 millimeters in diameter. Hatchlings of _spinifer_ have ovaries that measure approximately 6.0 × 0.3 millimeters, and straight oviducts 0.2 millimeters in width (TU 5988, plastral length 3.5 cm. measured with ocular micrometer). In the size at which sexual maturity is attained there seems to be much individual variation as well as geographic variation.