1924-26 Watermark Block Cypher 2½d. blue Control 'O 31', S.G.N37(1),

horizontal marginal block of 6 from the lower left corner of the sheet, Control 'O 31', Imperforate margin, fresh, a few split perforations between the first and second columns at the top, large part original gum. AN EXTREMELY RARE CONTROL BLOCK.