Here's a One-and-two-thirds-dollar bill

Found in the collections of the National Museum of American History at the Smithsonian.  The photos are of marginal quality, but are supplemented by this description:

The note is worn, and, in common with several of its fellows, it was carefully stitched together, obscuring part of the design. But if we could see everything, we would see that, on the front of the note, a figure representing Great Britain receives a petition of the Continental Congress. It is handed to her by an America, who is simultaneously trampling on a scroll marked SLAVERY and holding aloft a Liberty cap on a pole, a beacon for American troops who are hastening to the scene from the right.

Meanwhile, George III (the figure at the center-left) is doing his best to set fire to an American city (perhaps Baltimore) already under attack from a British fleet. He's also trampling a copy of Magna Charta, just to underscore the point. Inscriptions along the sides read "AN APPEAL TO HEAVEN" and "PRO ARIS ET FOCIS" (For altars and hearths). The other side of the note conveys hope. Britain and America are shown achieving peace, with the reminder that "PAX TRIUMPHIS POTIOR" (Peace is preferable to victory).

The note was designed by Annapolis silversmith Thomas Sparrow in the summer of 1775. His initials are inscribed on the front and his full name on the back. This series of Maryland notes remains the most politically charged currency ever issued in the United States during wartime.

That explains the design, but not the curious denomination.  There were no American "dollars" until 1792, so the dollar referenced in this bill would have been the Spanish one.  But why have the bill in such an odd multiple?  Any numismatists out there have ideas?