Silver Dollar Mk.35 is a shotgun used by Guardians. The weapon is built on a sturdy frame that can accommodate a number of variations of attachments and accessories, but the Silver Dollar Mk.35 comes with a catcher and a four-cartridge sidecar.
Its paint scheme seems to imply that "it has seen action near the evacuation site for the last colony ships that escaped the collapse."
This weapon has been shown only in screenshots and described briefly in an article on Bungie's official website. Despite having been removed from the final game, it is still present on the Shotguns Grimiore card.