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From what I know there are few cuts of pork shoulder - the top part (Boston butt and most common in BBQ). Then there is a cut which includes the front leg quarter of the hog or the shank. Sounds like you got the one with the shank. Usually this one has a bit of the skin on and is called a picnic... can you send a pic?
Ohh and I have heard they are cooked the same just trim some of the fat (not all of it will "melt" into the meat and its easier for me to remove it before I cook it than after its been cook (but careful to not cut off too much) - there is great debate on which taste better (most say the picnic is better) but the butt is cheaper...