Listen to Chelys sonora, Op. 6: Concerto No. 21 in C Major: I. Allegro online. Chelys sonora, Op. 6: Concerto No. 21 in C Major: I. Allegro is an English language song and is sung by Monteverdi Ensemble Wurzburg. Chelys sonora, Op. 6: Concerto No. 21 in C Major: I. Allegro, from the album Rathgeber: Missa St. Benedicti, was released in the year 2010. The duration of the song is 2:16. Download English songs online from JioSaavn.