Does your Krause catalog have a pictorial chart of all the mintmaster marks, at the front of the France section, which might ID that little beastie below the bust? I no longer own the paper catalogs, and the NGC/Krause/Numismaster online database is kind of sparse with details like that.
The type which @chuckylucky5 identified is 23 mm, so I dunno. Was there another slightly larger denomination? Hmm... Edit- oh, wait- I just linked up the wrong type. That one has the denomination "XX" in the field. Never mind.
I think this is it... 1/3 ecu. Diameter 26.5 mm. "A" mintmark (Paris) below the point of the shield. I'm pretty sure the little critter and shamrock thingie below the bust would be the mintmaster's personal symbols.
According to Krause, the catalog value for the 1720-A 1/3 ecu is disappointingly low. In that grade, with the old scratch across the obverse, this coin is likely worth less than ten bucks. Which is lower than I would have guessed, based on its old silver "coolness factor", and history. But the KM (Krause-Mishler) catalog values are often quite low on 18th century stuff, I've found. On eBay, such a coin could certainly fetch more than that, I would think. Not that you're intending to sell it, of course. It's a neat old piece. This is some cool stuff you've been posting. Must be fun to go through.
The animal shown under the king's head is a fox and is the mark of of the Directeur of the Paris mint Mathieu Renard de Tasta, 1719 to 1738. The shamrock is the mark of the engraver, Pierre Rousseau, 1674 to 1679, whose design was still in use
