Today is the feast of SS Perpetua and Felicity. It is of double rite. Today is also Ember Friday in the first week of Lent. The day is typical of a Festal Office in Lent.
At Mattins the invitatory and hymn are from the Common of Martyrs. The antiphons and psalmody are taken from the Psalter for Friday, the antiphons being doubled at Mattins and Lauds as the feast is of double rank. As the Lenten weeks do not have Scripture for the first nocturn the lessons are taken from the Common, Confitebor etc, with the responsories also coming from the Common. In the third nocturn the ninth lesson is that of the Ember Day. Normally the ninth lesson of the feast was omitted and the first lesson of the commemorated ferial day read as the ninth lesson. in its place. The better practice was to combine the ninth lesson of the feast with the eighth lesson and then, for the ninth lesson read all three lessons for the Ember Day together as the ninth lesson. The Te Deum is sung.
Again at Lauds the antiphons and psalms are from the Psalter for Friday (the first scheme of psalms). The chapter, hymn, versicle & response and antiphon on the Benedictus are from the Common. After the repetition of the antiphon after the Benedictus the Ember Day is commemorated. Its antiphon and collect are proper.
At Prime the fourth pslam is not added. The chapter is the festal Regi saeculorum, there are no Dominical preces (as the feast is of double rite) and the lectio brevis is of the feast, Laudabit.
Mass follows Terce. The Gloria is sung, the feria is commemorated, the preface is that of Lent and the last Gospel is of the Ember Day.
Private Masses may be of the Ember Day, with a commemoration of SS Perpetua and Felicity, there is no Gloria, the dismissal is Benedicamus Domino and the ministers wear folded chasubles.
In Cathedral and Collegiate Churches, following Tridentine practice, a Mass of the feast follows Terce, without a commemoration of the feria. After None the Mass of the Ember Day is sung with the second collect A cunctis and third collect Omnipotens. Following the reforms of 1911-13 a Low Mass of the feast takes place without the chorales being present and Mass of the Ember Day is sung after None. Westminster Cathedral, as far as my understanding goes, carried on with the more authentic practice and had two High Masses, praeter legem.
Vespers, of course follow Mass in the morning, and are from the chapter of the following feast of St. Thomas Aquinas with a commemoration of SS Perpetua and Felicity, and of the feria. In the afternoon Compline is sung without preces.