St. Marcellinus was also a Roman. He governed the Church from 293 to 304, during the terrible persecution of Diocletian who caused him to be beheaded. The name of St. Cletus is in the Canon (first list).
Their Mass is that of Martyrs in Paschaltide. It shows how faith in the virtue of the resurrection of Christ sustains souls in the midst of the sufferings they have to undergo on earth after Christ (Epistle) before sharing in His triumph in heaven (Intrcit, Epistle, Gospel, Offertory, Communion).
Let us glorify Jesus, whose members we are, by producing many fruits of patience, as did these holy martyrs (Gospel).
Sancti tui, Domine, benedicent te: gloriam regni tui dicent, alleluia, alleluia. * Exaltabo te, Deus meus Rex: et benedicam nomini tuo in saeculum, et in saeculum saeculi.
Let the saints bless Thee, O Lord; they shall speak of the glory of Thy kingdom, alleluia, alleluia. * I will extol Thee, O God my King: and I will bless Thy name for ever; yea, for ever and ever.
(Psalm 144:10-11,1 from the Introit of Mass)
Beatorum Martyrum, pariterque Pontificum Cleti et Marcellini nos, Domine, foveat pretiosa confessio: et pia jugiter intercessio tueatur.
May the precious confession of the blessed martyrs and bishops, Cletus and Marcellinus, be our solace, O Lord, and may their loving intercession ever be our sure defence. Through our Lord.