Blazon: Quarterly of four: 1st: Quarterly 1st and 4th France modern and 2nd and 3rd England (royal arms); 2nd & 3rd: de Burgh; 4th: Mortimer; over-all a bend sinister; over all an inescutcheon of pretence of Grey, Viscounts Lisle, quarterly of six, 1st: Barry of six argent and azure in chief three torteaux (Grey, Viscount Lisle); 2nd: Barry of argent and azure, an orle of martlets gules (Valence, Earl of Pembroke), 3rd: Gules, seven mascles or conjoined 3, 3, 1 (Ferrers of Groby); 4th: Gules, a lion rampant within a bordure engrailed or (Talbot); 5th: Gules, a fesse between six crosses crosslet or (Beauchamp); 6th: Gules, a lion statant guardant argent crowned or (Lisle) Crest: On a cap of maintenance gules turned up ermine, and inscribed in front with the letter A, a genet guardant per pale sable and argent, standing between two broom-stalks proper.
Thus the fourth (Mortimer) quarter shows: Or three bars azure on a chief of the first three pallets between two gyrons of the second, over all an inescutcheon argent. This matches the Mortimer arms described in Boutell (pp 58/59). However the Wiki page also provides an image of Lisle's arms before his marriages:
with the following blazon:
[My emphasis]Arms of Arthur Plantagenet before his 1st marriage. They are his paternal arms, with baton sinister azure for bastardy, of Edward, 4th Duke of York, Later King Edward IV: Quarterly 1st: Arms of King Edward III; 2nd & 3rd: Or a cross gules (de Burgh), 4th: Barry or and azure, on a chief of the first two pallets between two base esquires of the second over all an inescutcheon argent (Mortimer)
Somehow the Or three bars azure on a chief of the first three pallets between two gyrons of the second, over all an inescutcheon argent. has been transmogrified into Barry or and azure, on a chief of the first two pallets between two base esquires of the second over all an inescutcheon argent. Moreover the same error seems to have been perpetrated with all the Mortimer Earls of March, including Edward Plantagenet who later became King Edward IV (and Viscount Lisle's father). And what on earth are "two base esquires"? Gyrons I understand, but "base esquires"?
I have put all this to the originator of the emblazonment, who goes by the moniker "Sodacan". He is a prolific provider of heraldic material to Wikimedia, so who knows, we may learn something. Meanwhile does anyone here know the correct blazon for the arms of Mortimer, and what (if anything) are "base esquires"?