Some aspects of the reproductive behaviour and genital structures of Z. petiolatum are described from observations made at Madurai in southern India. Sexually active males patrolled continuously over small permanent pools from about 45 min before to 10-15 min after sunset, interacting aggressively with other males. Copulation was brief and aerial, and it was immediately followed by guarded epiphytic oviposition. A few immature individuals commonly appeared in flight at the water from about 10 min after sunset, remaining there until after the departure of all sexually active dragonflies. — Females possess extended and cleft sub-genital plates and males have correspondingly elongated hamules. Internally females are equipped with a relatively small bursa and a pair of spermathecae supplied through a T-shaped duct. The penis bears a pair of partially inflatable cornua and a bifurcated flagellum. Each branch of the flagellum terminates in a large hook and has a helically twisted membrane running along its outer margin. Some functional interpretations of these structures are discussed. The behaviour and morphology resemble those of Tholymis tillarga which occurs in the same region, but the species do not normally share the same habitats.