You appear to have on your hands a French epée style bayonet. My best guess, without being able to handle it and give a closer inspection, would be a Model 1886, as that matches the appearance in the photos and the length you provided. It remained the basic pattern for French bayonets through WWI, although later revamps would drop the big hooked quillion that makes it distinctive, so it wouldn't be seen on a pattern 86/93 or 86/93/16. It would have been initially issued for a Lebel rifle, but interchangable on other rifles France adopted in the period, most especially the Berthier.