U.S.P.O., Philadelphia Pa., 1c Black on Blue Glazed (7LB7).
Large bottom margin, uncancelled, used on blue folded cover to Alexandria Va., blue "Philada. Pa. 5 cts. May 31" (ca. 1850) integral-rate circular datestamp, stamp has slight rubbed spots along corner creases, otherwise Very Fine, very scarce (17-18 covers reported by Lyons), ex Caspary and Middendorf
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