I'll try to post up a photo of the mount.

Sounds like they're worth doing something with....Any idea how they would compare quality-wise with Nikkor lenses? Firstly if it's possible to use them with my Nikon body, and secondly e.g. with a Praktica body?

Flotsam, I think you're right about the 'Jena' bit, - it would have been the E.German side, as I believe they were originally aquired after the fall of the Wall.

Many thanks for your help!