Bermuda 1918 KGV High Values Mauritania Archive Specimens Unique

MAURITANIA UPU ARCHIVE RECEIVING AUTHORITY SPECIMENS: 1918 KGV High Values 2/6, 5/-, 10/- & £1 (SG 52-55). All in strips of three, each stamp overprinted SPECIMEN Type D12a in the usual manner for the UPU, affixed together to portion of ledger page and additionally handstamped with large part 3-line "SPECIMEN / COLLECTION / MAURITANIE" in red-purple. Sent from the UPU in Berne to the Mauritania Post Office where they were affixed to the ledger page and tied by the Mauritania handstamp. Minor imperfections as usual for these. A unique and philatelically important group, a magnificently colourful array!