Zeiss 50mm f2.8 enlarger lens

How do I mount this lens on a 35mm Durst B&W enlarger?
I 've got a Nikon EL that has a ring attached, one that doesn't screw on the the Durst but simply because it has a larg diameter it mounts without using a thread of some kind, no screw or bayonet/just locks.

Here is a better shot of the back side of the lens

Never heard of a Zeiss 50/2.8 enlarging lens...does it have aperture blades even? Interesting looking thing.

Can you send better pics of what's written on this lens?