I see more bowed psaltery(s), but I believe you might have a fretted psaltery. There are many variations on the theme, but this one seems to fit the category. Stuart
Bingo, Dave! That's a great photo. Remarkable. The faint pencil scratches inside look like someone's initials and the numerals 77, possibly standing for the year 1877, but I'm just guessing.
Thank you SO MUCH for posting your reply and this photo. Now I know! It's a streichzither!