IV class
White
The First Thursday votive Mass may be said: “one Mass of our Lord Jesus Christ, eternal High Priest, on the first Thursday or the first Saturday of each month, in churches and oratories in which special devotions are held on that day for the sanctification of the clergy” (Rubricæ generales, 385a)
Mass of the feria (White); use Mass of January 1 (in Octava Nativitatis Domini); Gloria; no Credo and no proper Communicantes; preface of the Nativity
OR
First Thursday votive: (White) Mass of our Lord Jesus Christ, eternal High Priest, Gloria, no Credo, common Preface
The principal parts of the office during these seasonal ferias are from January 1, but are all listed together for convenience in the Ordinarium, under Time of the Nativity
Matins: Invitatorium and Hymn from the Time of the Nativity; psalms and antiphons of the feria; scripture lessons proper to January 2; Te Deum
Lauds: Psalms and antiphons of the feria; capitulum and following from Time of the Nativity
Prime: Psalms and antiphons of the feria; Verse Qui natus es
Hours: Psalms and antiphons of the feria; capitulum and following from Time of the Nativity
Vespers: Psalms and antiphons of the feria; capitulum and following from Time of the Nativity
Compline: Of the feria
IV class Votive Masses are permitted, but IV class Requiem Masses are not (until January 13 inclusive)