|00:33The classic blues guitar is the resophonic instrument developed around 1930 by the National Reso-Phonic Guitar Company. These instruments are powered by an aluminum cone surmounted by a wooden bridge over which the strings pass to deliver their vibration to the cone. The biscuit supports the bridge, sometimes called a "biscuit bridge."
That black wooden disc on top, depicted in the photos, is called the "biscuit," and the assembly is often called "biscuit cone." The bridge is the vertical piece in the middle of the biscuit.