Sorry to be so slow on the draw, SS. The Thuc line of bishops is just the line which 'originated' with Abp Thuc, an early resister to V2. Some (erroneously) hold that line to be invalid for various, worthless reasons. If you want more info, let me know. However, I will warn you it is one of the many mega-dramas of Traddieland and you may not want to bother with wading through all/most of the material. I could give you the condensed version, but not tonight...