Sinar Norma Automatic Iris mount.
All Sinar gear is amazing. Great precision stuff and pleasure to work with. Their pan and tilt heads are probably the best heads I have ever had and can deal with anything you throw at them. The same with the rotating holder that I am lucky to have - it can take up to 60kg of gear and have it swung around its axis with amazing, micrometer precision.
Also, the automatic shutter (the early version pictured on your photo) is absolutely a genius thing - you can have just one shutter for all your lenses and set the aperture with ease. Sinar put so much thought in their systems' modularity and usability.
Also, the workmanship and quality is top notch - their products can serve a lifitime or two.
It is a pity that they are no longer in business.