Elongation of the preanal region of the tail resulting in the extension of the cloacal opening beyond the posterior edge of the carapace occurs in males of several kinds of turtles, including _Trionyx_, at least in those from Louisiana, Texas, and Lake Texoma, Oklahoma (Webb, 1956:121). Probably this elongation is characteristic of males of all American softshells. Some females of _spinifer_ and _muticus_ that exceed the maximum size attained by males have the tip of the tail and cloacal opening extending a short distance beyond the posterior edge of the carapace. Some large females of _ferox_ have more elongate tails than those of _spinifer_ and _muticus_. _Width of Alveolar Surfaces of Jaws_ Stejneger (1944:34-36, pl. 6) commented on a series of large skulls of _ferox_ mostly from Kissimmee, Florida, some of which had conspicuously expanded alveolar surfaces. He suggested that the condition was confined to large males. A scattergram (Fig. 2) based on measurements obtained from 45 skulls of _ferox_ shows widened alveolar surfaces of the upper jaws on some of the larger skulls. Because the maximal size of adult males is unknown and the difference in size between the sexes of _ferox_ is slight, such large skulls might represent either sex. The sex had been recorded for only three of the 45 skulls; none of the three exceeded 82 millimeters in basicranial length or had widened alveolar surfaces. Some of the larger skulls of approximately the same size differ markedly in width of the alveolar surfaces; this difference suggests that both sexes are included and that the sexes may be of approximately the same maximal size. On the other hand, the variation observed in skulls is possibly confined to one sex. To judge from what is known of the maximal sizes of the sexes of _spinifer_ and _muticus_ (see Table 2), skulls of _ferox_ of more than 85 millimeters in basicranial length probably are of females. The largest alcoholic male (dissected) of _ferox_ that I examined had a width of head of approximately 46.5 millimeters; that measurement corresponds to a basicranial length of 70 to 75 millimeters. The specimen of which measurements are depicted by the uppermost symbol in the scattergram (represented by KU 16528) was recorded as a female. Large females of _T. s. asper_ from rivers emptying into the Atlantic Ocean have broadened alveolar surfaces. [Illustration: FIG. 2. Basicranial length and greatest width of alveolar surface of upper jaw on 45 skulls of _T. ferox_. Some skulls (sex unknown) in which the basicranial length exceeds 85 mm. develop widened alveolar surfaces of the jaws.] _Length of Claw_