... Now I'm confused Is this not volume I (tome premier)? ...
You are right, it is Tome 1,Volume 2.
But the numbers aren't unique (I haven't been thinking about that, sorry), in this volume the number 888 occurs more than once because each region has it's own numbering
.
Hence a number alone is not a clear reference, the page should be added (or the region of the coin), so your coin is
Mionnet Vol I-2 page 584, number 888.
The
monograms for the first series of these books (not the supplementary series) are listed in a special volume.
Monogram 168 can be found here:
https://gallica.bnf.fr/ark:/12148/bpt6k3990868/f138.imageit is the last one on the page.
Regards
Altamura