From December 18 to 23, III and IV class votive and Requiem Masses are prohibited.
No Gloria nor Credo; common Preface; Ite, missa est.
N.B. More information on Ember Days and particular rubrics on the Flectamus genua can be found in Rubrical FAQs.
Matins: Invitatorium Prope est iam; Hymn Verbum supernum; Saturday psalms and antiphons; no Te Deum
Lauds: Saturday psalms of the 2nd scheme; antiphons are proper (they are given in the psalter: Sabato ante Vigiliam Nativitatis Domini); Hymn En clara vox; preces. Nota bene: the Benedictus antiphon is proper to December 23 (printed in the proper section after the III Sunday of Advent): Ecce, completa sunt * omnia, quae dicta sunt per Angelum de Virgine Maria.
Hours: Saturday psalms with antiphons from Lauds
I Vespers: Of the IV Sunday of Advent; Hymn Creator alme siderum; Magnificat O Emmanuel (O Antiphons for Advent). (The IV Sunday of Advent will not be celebrated, as it yields to the Vigil of the Nativity, but I Vespers of the IV Sunday is used this evening nonetheless because the Vigil does not have its own I Vespers.)