Abstract: A geneva mechanism has a slotted geneva wheel and a driving cam wheel engageable with the geneva wheel to impart stepwise rotation thereto. The geneva wheel carries rollers, two of which are simultaneously engageable by a first part-cylindrical surface on the cam wheel to lock the geneva wheel against rotation. This simultaneous engagement imparts a slight resilient stress to the parts and thereby prevents backlash movement during the locked condition. Additionally a second, parallel part-cylindrical surface on the cam wheel co-operates with the first such surface and with two of the geneva wheel rollers to maintain the geneva wheel under control of the cam wheel as the latter starts and ends its driving engagement.