Thanks Dan.
Lee, you got the question (and the answer) right.
This is a third cam lens, also known as "R-only", but doesn't say so in white letters as others I have seen.
As Lee says, will not mount on any Leicaflex model but will be fully functional on Leicas R3,4,5,6,6.2 and 7.
As far as I know, will mount on Leica R8 and 9 and work at least in some operational modes (because it has no ROM).