1844 Z1-C is a crude, hand-made Seated dime die marriage which is considered a singleton. It was struck on a German silver planchet with a reeded edge. Currently only 5 examples have been documented, and most look similar to the example here. The example here was also the Plate Coin in the most recent Bad Metal silver book.
 
Nearly all hand-made die struck Seated dime varieties are rare, and examples like this rarely come up for sale. Personally, I'm trying to acquire other varieties for my collection but nobody wants to sell their examples because replacing pieces is next to impossible.