Looks like a JP Gemmer conversion. I've seen them mostly on Sharps rifles, but have never owned one. I think they're a neat look, though, for someone who likes that transitional era of gun history.
Have no clue about the gun but do have a question about the picture... why is there a cartridge shown and the rifle has a ramrod under the barrel? I guess maybe that is for cleaning it .... like the rod on an SKS?
If the gun is black powder cartridge, I would guess its to swab the barrel every few shots. All of my military rolling blocks had a cleaning rod under the barrel