Saint Michael, Archangel, defend us in battle.
Be our protection against the wickedness and snares of the Devil.
May God rebuke him, we humbly pray;
And do thou, O Prince of the Heavenly Host, by the power of God, thrust into hell Satan and all the other evil spirits who prowl about the world seeking the ruin of souls. Amen.
-- Pope Leo XIII
Appropriate lectionary readings can be found here. Michaelmas is one of the quaterdays and is associated with the Autumnal Equinox.