Well dawggone, Wild Bill! I had a pair of those Shu-Lok snap-open shoes. I'd forgotten all about them. A piece of metal kind of like a shoe horn without the handle part was sewn inside the tongue. There was some kind of spring mechanism so that when you pulled on the tongue it rotated up with a click, then snapped back into place when you pushed it down. (Added later: it acted like the mechanism used for men's snap-on ties) I think the idea was to avoid breaking down the back of the shoe while slipping it on.
Link to the book:
Wild Bill Hickok 02 (Blue Bird)