cover 1875 (18 May) envelope from Armagh to Peking "per French Packet" bearing G.B. 3d. and 1/- tied by the despatch duplex cancellation  and showing "PD" in oval, the reverse bears a good strike of the scarce type 6 "HONG-KONG TO/SHANGHAI" Marine Sorter dated "JY 29/5 75" along with a large part strike of double-oval "CUSTOMS HOUSE/PAID/SHANGHAI" dated 1875 (5 July) in red (31x22.5mm). Sadly part of the flap has been torn away, nevertheless a very desirable cover. Photo
CHINESE EMPIRE Postal History and Stampless Covers Shanghai Customs House Paid
cover 1875 (18 May) envelope from Armagh to Peking "per French Packet" bearing G.B. 3d. and 1/- tied by the despatch duplex cancellation and showing "PD" in oval, the reverse bears a good strike of the scarce type 6 "HONG-KONG TO/SHANGHAI" Marine Sorter dated "JY 29/5 75" along with a large part strike of double-oval "CUSTOMS HOUSE/PAID/SHANGHAI" dated 1875 (5 July) in red (31x22.5mm). Sadly part of the flap has been torn away, nevertheless a very desirable cover. Photo

Details
cover 1875 (18 May) envelope from Armagh to Peking "per French Packet" bearing G.B. 3d. and 1/- tied by the despatch duplex cancellation and showing "PD" in oval, the reverse bears a good strike of the scarce type 6 "HONG-KONG TO/SHANGHAI" Marine Sorter dated "JY 29/5 75" along with a large part strike of double-oval "CUSTOMS HOUSE/PAID/SHANGHAI" dated 1875 (5 July) in red (31x22.5mm). Sadly part of the flap has been torn away, nevertheless a very desirable cover. Photo
Further details
The Customs House is a rare marking, only eleven covers are recorded in Revenue Surcharges vol. II, these are all outbound covers with earlier dates than this and apparently two different sizes; Webb's Scarcity Guide records five or less of the Marine Sorter (though more exist)