Witches of Thessaly
The Witches of Thessaly is an Ex Miscellanea tradition descended from the Daughters of Erichto - a pagan tradition practicing dark, possibly Infernal, magic. Some witches remain in contact with their non-Hermetic brethren, which causes concern about diabolism in their ranks. Notably, Trianoma was also descended from the Daughters.
The Daughters of Erichto are sometimes also, confusingly, referred to as Witches of Thessaly. It is possible that they are part of the same Infernal Tradition.
The tradition is provided as an "idea" for an House Ex Miscellanea tradition in Houses of Hermes: Societates 109. See also Realms of Power: The Infernal 140 for more details on the Daughters and Witches.