Auction 333-341 Nigeria, Cameroon, Sudan & Worldwide Postal History - Day 4

1893: Postal Stationery, 1 d. carmine, reply part of card, perf. 7, used from West Hartlepool, England to Zanzibar, East Africa, dated 7 April 1897, cancelled by a double circle "WEST HARTLEPOOL" in black, with "ZANZIBAR" cirrcular datestamp alongside also in black dated 6 May 1897. Long message to the reverse. Slightly rounded corner lower right, otherwise fine. A rare usage contrary to regulations.
Note: According to the UPU regulations, response cards could only be sent back to their originating country and cards sent elsewhere should be treated as not franked. 
Reference: The Postal Stationery of Nigeria, by Peter Hørlyck, illustrated pg. 20.