I posted about this a couple years ago on a Marlin collector's site. It's a prototype completely functional receiver for a single shot based on Marlin 22 caliber pump action repeaters. About the only mention of these is in Brophy's book on Marlins where he says there is no indication that they ever tried to put them into production. It was during the Marlin-Rockwell years.
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The cost had to be high compared to most other single shots at the time. Looking at the details, they tried to cut production cost by making the top & bottom tangs the exact same straight contour to simplify machining and eliminated the machined step in the top of the receiver found on all the other pumps. These parts are not modifications of parts intended for a repeater. Even the locking arm is specific for a single shot since it's not milled for the parts needed to work a lifter.

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The only picture of one that is not just a modification of another model of receiver that I've ever found is the one pictured in Brophy's book on Marlins.
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The patent was applied for Dec 3,1921 but not issued until 1926.
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