1909, 5¢ blue, bluish paper, top left corner margin single with siderographer's initials at left and manuscript "X" control in corner selvage, o.g., only the barest trace of hinge on lower right corner, precision centering amid well balanced margins, bold color on deeply blued paper, Extremely Fine and choice, a magnificent and likely unique corner margin example of the 5¢ bluish paper issue, quite certainly One of the Finest Known Examples in Existence; with 1978 P.F. certificate for block and 2002 P.F. certificate. Scott No. 361  $5,750. $0 (Image)