Don't ask me why Campagnolo made an Euclid rear derailleur, but that sure does look like what we have here.  eBay Seller pb*bikes had the box and everything, and the cage on this NOS derailleur was obviously shorter than both the Long and Medium cage examples already listed.  I have cleared the Max Cog and Chain Wrap values until they can be verified.

The hardened steel adjusting screw presses on a mobile steel bracket which varies the preload of the tension spring. The less the spring is preloaded, the tighter the chain wraps the freewheel, thus promoting quicker more accurate shifts. Between the mobile steel bracket and the body of the rear derailleur is a special anti-friction bushing which significantly reduces pivot friction and ensures the precise, flowing movement of the rear derailleur.