block of four (positions 29-30, 39-40), top left stamp inverted "M" in "Panama" (11.1) and top right stamp left "Panama" 16mm long (11.2), used alongside 1906 2c on 1p Lake (17) on registered cover to Dr. Perry in Ancon, Cristobal April 24, 1906 registry handstamp and backstamped Ancon the following day, very fine and choice, ex-Plass