At age 43 Bishop van Lierde was appointed successor of Bishop Alfonso de Romanis, OSA, who since 1937 had been Sacristan of His Holiness and Vicar General for the Vatican City State. Van Lierde was therefore consecrated bishop in 1951. His duties as sacristan included being on hand for the daily Mass of the pope and serving the Mass, if needed. In the image above he can be seen holding a candle for a liturgy at the Lateran Archbasilica.
Due to longstanding tradition going back to the end of the thirteenth century, the sacristan of the Papal Palace was a privileged member of the Order of St. Augustine. This office was entitled with certain privileges, including this version seen here of the abbreviated cappa magna. It was tailored in Rome in black wool and ermine, seen above on the figure of Bishop van Lierde. The side stole was originally the train, tied to signify that the beneficiary had no jurisdiction. Other times he is seen in a black mantelletta, as seen below.
In some ways his cappa parva resembles the "cappa" of other canons (seen below), including the "cappa fluens" seen in the See of Milan, used by Ambrosian provosts (pastors) and canons. Or the cappa parva of the canons of Westminster Cathedral in London, who have the privilege of the Lateran choir dress.