K. A. Heinrich Kellner, Heortology (1908)
“ With regard to the Roman rite in particular, there are no special masses for the Sundays after Easter and Pentecost in the Leonine sacramentary. A further development appears in the Gelasian sacramentary, where the Sundays in Lent and those between Easter and Pentecost alone have a clearly defined liturgical character, and keep their special place in the Calendar. ”
