I am currently investigating Catholic/Protestant theological differences. In trying to understand arguments about the immaculate conception of Mary, I began reading St. Thomas Aquinas, when I stumbled across something unusual. In Summa Theologica, Part 3, Question 7, Article 1, Aquinas addresses the issue of Mary's sanctification before birth. Aquinas references St. Augustine, supposedly in a work on Mary's Assumption:
I answer that, Nothing is handed down in the canonical Scriptures concerning the sanctification of the Blessed Mary as to her being sanctified in the womb; indeed, they do not even mention her birth. But as Augustine, in his tractate on the Assumption of the Virgin, argues with reason, since her body was assumed into heaven, and yet Scripture does not relate this; so it may be reasonably argued that she was sanctified in the womb.
My question is this: Did St. Augustine write a tractate on the Assumption of Mary?
I am aware that the Assumption is generally considered a late belief (and the earliest explicit quote I could find is from Epiphanius in 350AD, although it is debated). I imagine if a father as prominent as St. Augustine wrote a whole tractate on the belief, that would be a major piece of evidence. Is it perhaps a lost work of his, or maybe a medieval forgery that Aquinas thought was real? Any information would be appreciated.