What you have is an old spur trigger pocket revolver, or about half of it anyway. Without any markings, which would likely have been on the barrel I'm afraid I can't give you much more info than that. It will date to probably 1870's to around 1900 or so, probably in the earlier part of that range. It would have been a .22 given it's size.
They were made by a lot of different companies but yours would likely have looked like one of these two when it was whole....