A US Offices in China 1886 cover is expected to provide the leading lot at a major stamp auction in Switzerland later in the month.
The cover, which was sent from the USS Palos / Asiatic Station to Washington DC, bears a 5c brown Garfield featuring an oval killer bar.
The reverse reveals a pair of 3c lilac Small Dragon issue stamps on the reverse, which have been tied by the Tientsin seal.
It is currently selling for $21,958 ahead of the February 27 closing date for online bidding - already within estimate - a testament to the lot's significant rarity. It is the third earliest known Small Dragon / US combination cover and one of only 13 Small Dragon covers from 1886 recorded by Dr Kong Shiu-Ping.
The auction house has described it as "an extremely early and highly important Small Dragon / US combination cover of exhibition quality".
The USS Palos spent the majority of its 23 years of active service between 1870 and 1893 based in Chinese and Japanese waters.
Live bidding on the lot will take place on March 1.
Also starring is a US 15c brown and blue type II error from the 1869 pictorial issue. The centre-inverted, lightly cancelled stamp, whose two small tears on the right hand side are its only detractions, has an $8,235-$8,784 estimate.
The sale will also feature a 1962 China Mei Lan-fang souvenir sheet. The very fine, never hinged, original gum stamp has a $13,176-16,469 valuation.
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