Thank you for showing this, Chris.
Such an unusual and distinctive design, and so similar to the image in the Davidson catalogues of unregistered designs 18180-1890 (plus the fact that it is in marbled glass) that I imagine there to be an extraordinarily high probability that it is indeed pattern 52.
This must be quite a rare pattern - nice find.
I will add your pics (with a link to this topic thread) to the Glass Queries Gallery Davidson pattern database this afternoon when I get back from my volunteering stint.
Fred.