Abstract: In a photographic camera, a cassette carrier having a chamber for receiving a film cassette is movable outwardly from the camera body to permit one to insert and remove the film cassette. A drive spindle for the film cassette and a coaxial gear are rotatably mounted on a spring-urged slider supported on the carrier. Datum projections extend from the camera body to enter the chamber when the carrier is moved to return the chamber to inside the camera body, to shift the cassette from a centered position in engagement with the drive spindle to a datum position in the chamber. Simultaneously, a datum stop located in the camera body abuts the slider to shift the slider with the cassette and to limit the extent to which the coaxial gear will mesh with a driving gear rotatably supported in the camera body.