Whoever can identify this lens mount type is a badass.

Hints:
it's smaller than C mount and not threaded like D mount.
Appears on an angenieux retrofocus 6.5mm f1.8 and every link I found says this is a D mount. It does not have thread though and instead uses a locking mechanism similar to more recent lenses. Does not work with D mount adapters.

Close up of an unknown lens mount
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