The reproductive biology and diets of C. cautus, C. melanopterus and C. fitzroyensis from northern Australia are described. Males and females are usually mature at 84 and 91 cm, respectively, in C. cautus, 95 and 97 cm in C. melanopterus, and 88 and 100 cm in C. fitzroyensis. The species exhibit placental viviparity, have restricted breeding seasons, and individual females appear to breed annually. Breeding seasons for C. cautus and C. melanopterus are very similar: mating occurs between January and March, ovulation in February-March, and parturition in October-November. Individuals of C. fitzroyensis mate between May and July, ovulate between July and September, and give birth the. following February- April. Gestation periods for the three species range from 7 to 9 months. Approximate sizes at birth are 40 cm for C. cautus, 48 cm for C. melanopterus and 50 cm for C. fitzroyensis. Mean litter sizes are 2.9 (range 1-5) for C. cautus, 3.8 (range 3-4) for C. melanopterus and 3.7 (range 1-7) for C. fitzroyensis. Teleost fish are an important component of the diets, with crustaceans and molluscs (mainly cephalopods) of lesser importance. Snakes are eaten by C. melanopterus and C. cautus.