This type of mount is now usually called the "Holland & Holland mount". It is essentially a single-foot claw mount attached to the left side of the receiver. It works the other way around than the usual German claw mount: You first slide the rear foot into it's recess, where it hooks around a pin. then the front foot is swung down and secured by turning a small lever. The rod under the scope is there to keep the rings at the correct distance, even if the scope slips in the rings. H&H introduced this type of mount in the 1920s afaik.
Virtually the same type of scope mount was used several years earlier by by the Austrians on some of their WW1 Mannlicher M95 sniper rifles. The only obvious difference: the Austrians did not use such a "distance rod". As their rings were soldered to the scope tubes, they could not slip and such a rod was unnecessary.
Same question as with the Greifelt and Griffin & Howe single-lever sidemounts: who invented what and who copied a proven design?