In all my many, many, years of collecting, I have never before come across this very old and very beautiful stamp. It is MNH (full gum), and has near perfect centering. I am unable to catalogue the stamp after intense effort. Any help will be hugely appreciated.
Wow! Schwarzburg-Sondershausen was one of the smallest states that made up Germany at that time. It's amazing how they clung to their sovereignty and issued their own revenue stamps, but had their mails operated by either Thurn and Taxis (in this case) or one of the bigger states. Perhaps an early example of outsourcing ;-)