Tanganyika SG 55a 1917-21 GEA 1r emerald back Half sheet of 30

1917-21 G.E.A. 1r black/green emerald back Half sheet of 30 with plate number 1 showing variety Round stop after E on 5 positions (2/7 2/10 4/7 4/10) cat 450++ pounds 6 are m/m the rest are U/M. a few split perfs but overall if great condition Ex Pennycuick (Sothebys 22 Sep 1983 lot 976) when it was a complete sheet