The largest coins ever produced by the United States Mint, these $50 gold pieces were struck on the Philadelphia Mint's medal press which was shipped by rail to San Francisco for the striking ceremonies at the Exposition. Thus, these impressive coins bear the tiny 'S' mintmark of the San Francisco Mint, located at the lower right reverse. The obverse of Robert Aitken's magnificent design bears the date in Roman Numerals below the helmeted head of Minerva; the tipped back helmet signifies peace. The legend UNITED. STATES. OF. AMERICA. FIFTY. DOLLARS. encircles the obverse. The reverse features an owl, symbolic of wisdom, on a pine branch, surrounded by the legend, PANAMA-PACIFIC. EXPOSTION. SAN FRANCISCO. The eight dolphins in the corners were symbolic of America's desire to keep the Panama Canal open throughout the war. Fifteen hundred pieces were authorized and struck, but the selling price of double face value proved to be rather high. 483 rounds and 645 octagonals were sold, the balance were returned to the Mint for melting. The Round is thus slightly scarcer. This offering is especially appropriate considering the US lease on the Canal expires at the end of this year.