Back at Milepost 831, I had mentioned how the Old Wheeling & Lake Erie had a few camelback locomotives on their roster. But camelbacks weren't the only odd locos to grace their rails. From Mason Bogies (fixed-frame locomotives) to the "Fontaine" pictured above, the W&LE seemed to be home to some of the strangest contraptions on wheels and rails.
The theory behind the Fontaine is rather simple... the wheels mounted alongside of the boiler were larger than the loco's drivers, so every revolution of those larger wheels meant that the loco drivers would turn a little more than a full revolution. This would provide a little more spped and greater fuel efficiency. The locomotive was designed by the Fontaine Engine Company and two of them were built by Grant Locomotives in the early 1880s. While the patented friction drive mechanism may have worked in theory, the two main wheels often slipped. The two locomotives were eventually rebuilt to more conventional 4-4-0 wheel arrangements and remained in service until the turn of the century.
I don't model this time period but it would sure be a neat scratch-building project for someone who does. Starting with a traditional 4-4-0, I'd remove the cylinders then mount some slightly larger wheels astride the boiler as pictured. Re-attach the cylinders and you should have a pretty decent representation of this odd-looking character.