Unique “stacked” trigger configuration

[Snap Cap]

Tom, it is a Horatio Frederick Phillips trigger design patented on March 6, 1897.
It supposedly has at least four advantages according to the designer. It does not require regripping with the hand and sliding it on the stock like a one in front of the other double trigger gun. It prevents pulling both triggers when using a thick glove on the trigger hand. It does not require a separate action of moving a slide to select a barrel like a SST. It may prevent the involuntary discharge of the second barrel due to vibration that can happen on an SST gun. HTH FV.