single tied to 1904 cover to Dr. Mohr at the U.S. Public Health and Marine Hospital Service in Cristobal, July 27 Ancon datestamp alongside, stamp also tied by July 28 Cristobal datestamp, very fine and extremely rare with just two examples of this variety known on cover, ex-Plass, signed Perry and with 1996 Philatelic Foundation certificate (Scott $575 for used)