These two coins look very similar - a coat of arms on one side, Queen Victoria on the other. Neither actually state the denomination on the coin. Without a size measurement or comparison (something you often don't have when looking at a scan or pic on a computer screen), they can be hard to tell apart.

I've found the easiest way is to look at the obverse. On the sixpence, all the lettering of the legend is squeezed out to either side of the crown, on shillings the final A in GRATIA and initial B in BRITT are found hovering over the crown, between the crown and the rim.