This charming little device, with wooden frame and rear-mounted 500cc JAP engine was introduced in 1933. It does like it would be fun. The name came from the last names of the partnership, Jones, Mason and Barrow. It was pretty good for a first attempt, but in the next year many "improvements" were incorporated including a move to a steel frame, and metal replaced the fabric body panels. This added weight and cost which which affected performance and sales. The company made about 250 units before closing in 1935.
Apparently 4 remain in existence. More here.
Images from the Oct 1986 issue of The Classic MotorCycle.