American Flyer made the same thing for 3 rail. What you have is a #344 Automatic switch - it is spring loaded so a train approaching on the straight part heading into the switch will push the switch point and let the train pass after which the points return to the curved direction. A train approaching from the other direction will just go through the curve.
The earliest catalog listing I can find for the switch is 1927 and the last I can find is 1930. As NWL noted - it was part of a pair with the other switch as mentioned.