Do you see what it is, from the photograph showing it open?
We saw this at vintage and antique fare, we had to ask what it was, when we were told what it was, we bought it.
It is an early 20th century silver plated sovereign case, complete with chain for your waist coat.
We have cleaned it and replaced the material liner.
Having looked on e bay , we are very pleased with our purchase, comparing the price we paid with the price they sell for.