This essay discusses the order of grades of clergy alone. The Lorrha Missal cites nine divisions of the Church. These are given in the order for reception of Communion:

The Celebrant or Abbot Bishop of the Community.
The Bishops.
The Priests.
Lower Orders (Deacons and Subdeacons).
Monastics and Penitents.
Young Clerics (readers, accolytes, 'exorcists', doorkeepers)
Children.
Those truly penitent (unmarried adults)
Married persons and new communicants.

This number, nine, could also refer to the grades given below with the inclusion of accolytes and doorkeepers.

Curiously, the Romans view the Ostiaries as doorkeepers and set their rank as the lowest. The authors of the Bobbio Missal emphasised the role of an Ostiary as the keepers of the Crypts and holy relics and used the term for an Abbot or Archpriest in charge of relics.

"The first grade, Lector was made when He opened the Book of Isaiah and He said the Spirit of the Lord came upon Him.The second grade, Exorcist, was made when He cast seven demons outof Mary Magdalene.The third grade, Subdeacon, was made when He made wine from water in Galilee.The fourth grade, Deacon, was made when He washed the feet of the Disciples.The fifth grade, Presbyter (Priest), was made when He took the Bread and blessed and broke it and similarly blessed the Chalice.The sixth grade, Ostiary, was made when He said "Lift up your gates, O ye princes, and be ye lifted up, O eternal gates, and the King of Glory shall enter in."The seventh grade, Bishop, was made when He raised His hand over the heads of His Disciples and blessed them."

Translated by Fr. Maelruain Dowling, Céle Dé