Do you see that little lever/tab just in front of the barrel ring? That little do hicky plays a very big part in field stripping this gun. If you own one of these old shooters take your time figuring out how to break it down. If you do it correctly she comes right apart and unscrews easily. Remember she unscrews clockwise! (with the butt down looking from the muzzle end).
After fiddling with this interesting old Marlin I have come to the conclusion that the designer must have been French. In my experience French guns are always weird.