Males are lacking in C. rufum of the Salt Fork River near Homer Park, Illinois. There is no evidence of hermaphroditism. Stream collections throughout the year have been analyzed for information on growth and reproduction. Uterine young have shells 1.5-4.5 mm. in height. Parturition is most active in May but extends to about Sept. No young are liberated in nature or in aquaria in winter or early spring. The smallest free-living young are within the limits of size of uterine young, and the largest shells reach 40 mm. At one yr. the shell is about 22 mm. in height. The young, which spend about 9 mos. in the maternal uterus, are produced at the end of the 1st year. Size of shell is directly correlated with number of young. The largest shells seem to be 3 yrs. old. Seasonal studies of size of shell and number and size of young and of eggs are recorded.