Daryl,
If you look at the second photo you can see the nipple in the recess. I guess it was an early form of hammerless - well at least concealed hammer. They must have been a fiddle to cap but I guess the big advantage is that any fragments of copper cap or powder would not end up in your eye. I can put you in touch with the owner if you like who will be able to tell you much more about the gun. I only had a few minutes to take the photos and I would have loved longer to investigate these unusual mechanisms.
Have a look at...
https://www.facebook.com/AjB-Shoots-316395508394137/photos/?tab=album&album_id=1222848707748808
Photos taken by Amanda Broomhead who is a professional photographer so you can order anything of particular interest from her web site