The missing 13th. Concerns loss of citizenship if a title was bestowed (brief explanation). Looks as though it was ratified by 12 of 13 states for sure, except Connecticut. But this amendment is published in Connecticut statutes as part of the US Constitution thru 1835. Then it disappears.
http:// www.ptialaska.net/~swampy/amend_13/ amend ment.html.