Here's the Catholic Encyclopedia article on today's saint. Better yet, go read the wonderful essay on Mike Aquilina's blog, where "Cyril the Virile" is aptly described as "one of the odd uncles among the Church Fathers."
Father, the bishop Cyril courageously taught that Mary was the Mother of God. May we who cherish this belief receive salvation through the incarnation of Christ your Son, who lives and reigns with you and the Holy Spirit, one God, for ever and ever. Amen.