Hamon’s “Retroceps” by Mathieu circa 1860. A fine quality and rare instrument. See Kedarnath Das Obstetric Forceps page 411 which illustrates this very same model by Mathieu.
The left blade can be rotated and is anchored in position within the German silver handle by a fixed pin which fits into one of 4 holes in the steel disk at the proximal end of the blade. The right blade does not rotate but and be abducted or adducted by loosening or tightening the screw on the right of the handle.