Hi They are a kind of mute, they open by the rocker switch (in this instance) in the middle to allow a slightly brighter & louder sound to be heard than when closed. They mostly date back to c1960s, and can be seen on PSoprani, Scandalli and Parrot (and maybe others that I don't immediately recall, certainly also on some Russian models).
The Scandallis in nice condition I've seen with asking prices of £1000+
Pans (I call them) are usually the same, all do the same thing. It's possible the one has tarnished or been broken, and a replacement has been found that doesn't match the originals. The linked one has 4, 120 bass I've seen with 6.