The bike has some interesting details which made identification easy ... when in october 2012 I looked through a lot of antique bicycle catalogues in the Velorama museum. Most specific are the two stays which were used to attach the rear mudguard. And I found it in the catalogue of F. Mégret from Paris, the year is unknown but I guess 1892. Strange is that the catalogue calls it a childrens bike, with small wheels, while the illustration shows no children's bike at all. The bike of my French fellow collector even has the same saddle.
My conclusion: it must be an older model from F.Mégret, I guess 1890-1891. Maybe someday I'll find an older catalogue?