Lamb square-cut shoulder by John Spottiswood.

This is a tasty roast, but it's very hard to carve with the bone in. To make carving easier, butchers will bone it and sell it as a boneless rolled shoulder, or they'll slice the roast into blade chops and then tie them together as a pre-sliced shoulder roast = pre-carved shoulder roast. A pre-sliced roast is convenient, but it tends to dry out in the oven.