Mitsukuri (1905:265) reported that in hatchlings of _Trionyx sinensis_ the length of the carapace averages 2.7 centimeters (hatchlings of _sinensis_ seem to average smaller than any American species), and that the average length of carapace (cm.) at the end of the first year is 4.5, second year 10.5, third year 12.5, fourth year 16.0, and end of fifth year 17.5; he stated also that females of _sinensis_ are sexually mature in their sixth year. Breckenridge (1955:7-9) computed a growth curve based on 11 recaptures of females of _spinifer_ in Minnesota; his data on rate of growth for the first five years do not differ appreciably from those of Mitsukuri. As most females of _spinifer_ are sexually mature when the carapace is about 11 inches long, the age at sexual maturity is approximately 12 years according to Breckenridge (_op. cit._:8, Fig. 4). The discrepancy in age of females at the size of attainment of sexual maturity (Mitsukuri--six years; Breckenridge--12 years) is, in part, rectified by the fact that _Trionyx sinensis_ probably is a smaller species. Also, Breckenridge's computation of the growth curve is based on continuously decreasing increments of growth and seemingly eliminates consideration of the probable marked decrease in rate of growth that occurs when sexual maturity is attained--a phenomenon noted in other species of turtles. I think that increments of growth of immature turtles are, on the average, larger than those of sexually mature turtles. Judging from these criteria, the age of a female of _spinifer_ at sexual maturity is less than 12 years, and turtles having carapaces 17 to 18 inches in length (maximal size for _spinifer_) would be older than 53 years (_op. cit._:9). Occasional individuals, however, may greatly exceed the usual growth rate in which event large adults may be younger than 50 years.