The Dominican rite is a form of Mass that has remained unchanged since the 13th Century, when the Dominican order was founded. It is a variation on the Roman Rite that perhaps we are more acquainted with.
The differences between the Dominican Rite and the Roman are numerous and even vary within the expression of the Mass (Low, Sung or High). For example, at Dominican Low Mass, the celebrant wears the amice over his head until the beginning of Mass and immediately prepares the chalice upon reaching the altar.
He says neither the Introibo ad altare Dei nor the Psalm 42 Judica me, instead saying Confitemini Domino quoniam bonus, with the server responding Quoniam in saeculum misericordia ejus. St Dominic is mentioned in an abbreviated Confiteor. Both Gloria and the Credo are commenced at the centre of the altar and concluded at the Missal. At the Offertory there is a concurrent oblation of the Host and the chalice and only one prayer, Suscipe Sancta Trinitas.
The Roman Canon is used as per the Vetus Ordo, but the priest has slightly different postures for some parts of the Canon, his hands are folded, and immediately after the consecration, for the Unde et Memores, he also holds his arms in a cruciform position (a photo of this posture is shown below).
The Agnus Dei is said immediately after the Pax Domini and then are said the prayers Hæc sacrosancta commixtio, Domine Iesu Christe and Corpus et sanguis, then for the Communion, the priest receiving the Host from his left hand. No prayers are said at the consumption of the Precious Blood. I will briefly explain the use of the instrumenta pacis/Pax brede applicable at Solemn High Mass below.
Indeed, today's celebration was a solemn High Mass, hosted at the Santissima Trinità dei Pellegrini, the Rome Church of the Fraternitas Sacerdotalis Sancti Petri (FSSP). The celebrant was Rev. Fr. Dominique-Marie de Saint-Laumer, General Prior of the Fraternity of St. Vincent Ferrer.
Above I have attempted to explain some key differences as they occur at Low Mass, in the solemn expression of the Dominican rite the above occur but additionally, the chalice is brought in procession to the altar during the singing of the Gloria and during the Epistle by the subdeacon, the deacon unfolds the corporal and the deacon goes onto prepare the chalice after the subdeacon ends the Epistle.
The chalice is removed from the altar by the subdeacon and is taken to the celebrant who is seated on the Epistle side. The celebrant then pours the wine and water into it and it is taken back to the altar. Thereafter, some postural and positional variances from the Roman Rite occur and the incensing of the ministers occurs during the singing of the Preface unlike the Roman Rite.
At the Pax, the instrumenta pacis (sometimes called the Pax brede) is used. After the priest has dropped the particle into the chalice, immediately after the recitation of the Agnus Dei, the priest recites the mingling formula and kisses the chalice. The deacon approaches on the priest's right, takes up the instrument, and presents it to the priest to kiss. He then kisses the instrument himself and descends to the subdeacon. He presents it for him to kiss, saying Pax tibi et Ecclesiae Dei sanctae. He then gives him the instrument so that he can perform the same rite for the two acolytes. The subdeacon then proceeds to ‘give the peace’ to the friars in choir before returning the instrument to the altar placing it on the Epistle side of the corporal.
This was beautiful ending liturgy to a most wonderful number of days in the Eternal City to witness our Catholic Tradition.