Secondary sexual differences in length of claw on the forelimb are pronounced in some kinds of turtles. Cahn (1937:178) stated that the female of _Trionyx muticus_ usually has long claws on the hind feet, while the male has long claws on the forefeet, but I am unable to substantiate his statement. Measurements of length of the third claw on the hind limb taken in 41 males and 45 females of _spinifer_ from Louisiana showed no secondary sexual difference. Ontogenetic Variation _Pattern_ In all species and subspecies the juvenal pattern is replaced in females as growth proceeds by a mottled and blotched pattern that is contrasting or of nearly uniform coloration. The blotched pattern (of lichenlike figures) is evident on the carapaces of most females that have plastra so long as 8.0 centimeters. The contrasting juvenal pattern on the dorsal surfaces of the soft parts of the body is correspondingly modified in females, but at a size larger than 8.0 centimeters. Size of ocelli (OD/PL) in _T. s. spinifer_ and _hartwegi_ seems to vary ontogenetically (see section on Geographic Variation). Some hatchlings have blotched patterns (_T. spinifer asper_, TU 16689.2, plastral length, 3.5 cm.); the largest females examined that did not show any evidence of mottling were two _asper_ having plastrons 7.6 and 8.0 centimeters in length. Variation in color and pattern probably is modified greatly by the environment (Heude _in_ Stejneger, 1907:518, footnote d) and the physiological condition of the individual. Smith, Nixon and Minton (1949:92) reported that a female of _T. s. hartwegi_ developed a striking melanistic pattern in captivity and they concluded that patterns of soft-shelled turtles may be produced not only by conventional chromatophores, but also by other depositions, both intra- and extracellular. TU 16170, taken from brackish water at Delacroix Island, St. Bernard Parish, Louisiana, is the only adult male I have seen that had a blotched pattern (orange-brown in life) on the carapace in addition to the juvenal pattern. One female of _muticus_, KU 48229, having a plastral length 14.5 centimeters, retained a well-defined juvenal pattern, and lacked a mottled and blotched pattern (see Pl. 46). _Tuberculation_ Males of the subspecies of _spinifer_ develop small, sharp tubercles on the dorsal surface of the carapace when sexually mature. As growth proceeds, the minute prominences along the anterior edge of the carapace on hatchlings of both sexes of _spinifer_ change in shape to conical projections or low, flattened, scarcely-elevated prominences, depending on the subspecies (Fig. 8). Large females of _spinifer_ and _ferox_ acquire enlarged, flattened knobs in the nuchal region and posteriorly in the center of the carapace. _Length of Tail_ The preanal region of the tail rapidly elongates in males of all soft-shells when they are sexually mature. _Width of Alveolar Surfaces of Jaws_