HTH, Simon
Thanks Simon,
that's why the dots are weird (excuse the typo in my original posting).
O... would indeed multiply the duration of O by 15/8, but
O:. is intended to multiply the duration of O by 9/4 ( i.e. O. + ..)
I'm transcribing a piece without access to the original white mensural
notation, and I'm coming to the conclusion (for this and other reasons)
that the old edition I'm working from is seriously loopy. Time to
reverse-engineer the original notation and take a different approach
methinks...