Style wise, it looks like Rodenshtock Rodagon 2,8/50mm (enlarger lens).
Pentax standard hood perfectly fits on this filter-thread-less lens.
This hood > http://www.pbase.com/kkawakami/image/108526590

The lens does not have focus mechanism which is normal for enlarger lenses,
and that rubber ring is for the aperture setting. There is one more feature.