Of interest are the large females (for example, TU 13303, plastral length 28.0 cm.) that seemingly have immature, relatively small, ovaries (the oviducts are large and convoluted as in adult females). Possibly such ovaries represent a regression and are in senile turtles, but I am inclined to believe that the development of these ovaries has been arrested probably owing to hormonal unbalance, and that they have never been functional. The size of adult females of _T. ater_ is unknown but probably approximates that of _T. spinifer_ or is slightly less. Females of _ater_ 15.5 and 17.2 centimeters in length are immature; the largest female, the holotype, is 18.3 centimeters in length, and was not dissected. Females of _T. muticus_ are sexually mature when smaller than _T. spinifer_. Two turtles, 13.8 and 14.0 centimeters in length, have large convoluted oviducts about 10 millimeters in width and ovarian follicles nine to twelve millimeters in diameter, and seem to be near sexual maturity. The smallest sexually mature female (subspecies _muticus_) is TU 14436, measuring 14.4 centimeters in plastral length and having oviducal eggs. Recorded lengths of other adult females are 16.3, 16.5, 17.2 (subspecies _muticus_), and 18.0 centimeters (subspecies _calvatus_). Two females having plastral lengths of 17.5 (subspecies _muticus_) and 16.0 centimeters (subspecies _calvatus_) seem sexually immature. These turtles collected in April and May have ovarian follicles not exceeding three millimeters in diameter. _Sexual Activity_ Observations by Mitsukuri (1905:263), Conant (1951:160) and Legler (1955:98), constitute the extent of our knowledge concerning courtship and copulation. Legler observed a male _spinifer_ and a female _muticus_ in captivity; the male was the aggressor, following at the rear or above the female, and at times nipping at the anterior part of her carapace. During these movements, the posterior edge of the female's carapace was turned up slightly whereas that of the male was turned down; the turtles frequently surfaced to breathe. Occasionally the female followed the male. On the bottom the male crawled onto the female's carapace from the rear, remaining in a somewhat posterior position as described by Conant (_loc. cit._), and seemingly not clasping the female with his feet. Copulation probably occurs in this position; Mitsukuri (_loc. cit._) mentioned that copulation in _Trionyx sinensis_ occurs at the surface of the water. The male remains in the coital position for approximately 15 seconds and then slowly drifts to one side and swims away. Legler observed five coital unions in one-half hour, each preceded by courting movements. Legler's observations indicate that the courtship patterns of _muticus_ and _spinifer_ are similar, and that interspecific matings are possible. I have not noted any hybrid.