It is pretty defiinitely a Kerr, or a copy of one. Kerrs were made by the London Armory Co. and should have English proof marks. Since that one does not seem to have them, I think it is probably a copy, probably Spanish and converted to cartridge.
Here is a link that shows a nearly identical gun with an ejector added:
http://www.icollector.com/Spanish-Co...lver_i11083379
Jim