There's a reference to this project on the Chars de France website. Antoine Misner tells me it was a proposed machine "qui n'a jamais vu le jour" - which never saw the light of day.
All A.J. Smithers has to say on the subject is "plans for more and worse St. Chamonds followed."
It seems that this design was being considered as a replacement for the obviously unsatisfactory St. Chamonds & Schneiders, incorporating the advantages of the British-style all-round tracks. When the USA entered the War everything was dropped in favour of the Allied Tank Committee plan for Britain & the US to produce jointly the Mk VIII and the French the FT17.
Thanks for that tip, James, I've just had a look in Smithers. Interestingly, he says that 'A 40-ton affair was built in December, 1917; one of 70 tons was seriously suggested' (p.161). However, he doesn't say which of these projects was Schneider or St Chamond.
Now, Macksey's 'Tank Facts & Feats' from years ago has a brief entry on a Schneider project at the end of the Great War for a 141-ton tank with four 75-mm guns and gawd-knows-how-many machine-guns which was, needless to say, abandoned... Is this something else apart from those above mentioned by Smithers (could it have been '41-tons', and not '141-tons'?)?
I think I may have answered my earlier question of what A J Smithers was referring to when he wrote that 'A 40-ton affair was built in December, 1917; one of 70 tons was seriously suggested'...
Neither, of course, involved St Chamond or Schneider, which is what originally set me off thinking that he was referring to two completely unknown designs. Ah well, c'est la vie...
Meanwhile, good luck Tim with your question - someone must know more!