Your find is known by at least two names, an Aura or an Aeoline. But there is also a much larger musical instrument called an Aeoline. I dug one just like yours at a pre-civil-war Plantation site near Charleston SC. The photo and info below will tell you what you want to know. It was originally posted here in the What-Is-It forum by Creskol, so please give him the credit. I should mention, the one I dug is smaller than the dimensions in the photo... so apparently, they were made in more than one size. Please give us the measurements of yours.