The Medina Hawken patchbox lid is held shut by an 'over center' type closure like you'll find in the more common Hawken patchboxes. The cam is attached to the lid by two iron rivets on the center line of the lid and approx 3/8" apart and 3/8" from the main lid hinge. I believe it was opened with a thumbnail at the butt end.
Best,
John.