folded letter with sender's forwarding marking used as cornercard, carried by Cunard's America departing New York November 28 and arriving Liverpool December 12, marked "Not Known" in Ireland and forwarded to London Dead Letter Office, from there sent to the Dead Letter Office in Washington, DC where it was processed on May 17, 1851 (probably due to a large backlog of letters), returned to New York May 30, 17 months after originally being sent, very fine, transatlantic letters returned to the DLO are uncommon