Ireland. (Spain). Stamp-less envelope written from Sligo dated '22nd March 1851' addressed to Cadiz cancelled by Sligo double arc in blue with framed 'Paid at Sligo' on face, with m/s accountancy 'B-5/F-10 = 1/3' , endorsed 'via France' and routed via Dublin and London with French entry cachet and oval 'P.F.' (Paid to Frontier) and charged with hand-struck '18R' in red with disnfection slit and back stamped Cadiz '1st April'.