An inexpensive export grade fowler. Proof marks tell us it was made in or before 1804 while the K lock must date from 1793 or later. That's pretty good, placing it in about a 10 year time frame which isn't always possible. "Clark" is likely the merchant that sold it or, just as possible, the gunsmith that converted it.
I suspect it was full stocked originally. I say that because there is no nose cap and doesn't look as if it ever had one. It wasn't unusual for the long stocks to break and one solution was to cut them back and make a half-stock out of it. That said, half stock fowlers were also available so it's one of those conclusions based more on instinct than hard facts.
