PR.IA - standard windscreen, no armoured glass bolted on the outside.
PR.IB and C - rounded single piece perspex screen as per the earlier Spits but minus the inverted U at the front, like a shortened version of the Speed Spitfires one.
PR.XI - rounded single piece perspex screen as per the earlier Spits, different hood from the XI as it didn't have a pressurised cockpit.
PR.X - rounded single piece perspex screen as per the earlier Spits, a Lobelle hood however as it had a pressurised cockpit. This model went into service after the XI... weird! Only 16 ever made!
PR.XIII - Low-level PR, standard rounded single piece perspex screen as per the earlier Spits and armed with four .303 Brownings. Sometimes known as the Type G.
PR.XIX - Griffon engined monster! Again the rounded single piece perspex screen as per the earlier Spits and a Lobelle hood however as it had a pressurised cockpit.
I think that covers all the PR models
