If there are relics to be deposited, this is done after the Litany of Saints.
61. Then, if relics of the martyrs or other saints are to be placed beneath the altar, the bishop approaches the altar. A deacon or priest brings them to the bishop, who places them is a suitably prepared aperture. Meanwhile, one of the following antiphons is sung with Psalm 15:
Saints of God, you have been seated at the foot of God’s altar; pray for us to the Lord Jesus Christ.
The bodies of the saints are buried in peace, but their names will live for ever (alleluia).
Another appropriate liturgical song may be sung.
Meanwhile, a stone mason closes the aperture and the bishop returns to the chair.
The text of Psalm 15 is given in the 2003 ICEL draft (as are all the psalms).