Parry made two types of hammer doubles. The lower quality gun had a long frame and was bolted by a single "Greener" cross-bolt through the rib extension. The higher quality gun gun had Parry's rear-acting underbolt and the "Greener" cross-bolt. Within these "Qualities" the lowest grade gun had Twist barrels, the middle grade had Laminated barrels and the higher grade had Damascus barrels. Then there were special order higher grade Damascus barrel guns. There is an article on Edward George Parry by Bob Noble and the late William Achtermeier in
The Double Gun Journal, Volume Nineteen, Issue 1, that shows pictures by Daryl Hallquist of a very high condition single "Greener" cross-bolt gun. Serial numbers on Parry hammer guns seem to go up a bit into the 5xx range and from there on up to the 13xx range they are marked Wilkes Barre Gun Co.
Here is a Laminated barrel Parry with the rear-acting under-bolt --
