Above the niche are two marble angels, bearing the monogram of the name of Jesus in rock crystal, on a shield of lapis lazuli. In the tympanum is a group of the Holy Trinity in statuary marble, enthroned on clouds, and encircled with rays of glory, represented by gilt bronze. The Eternal Father, the Holy Ghost and the angel supporting the globe of lapis lazuli are by Bernardino Ludovisi; and the Redeemer, holding in his hand a gilt bronze cross, is by Lorenzo Ottoni.

(Another photo here)