Custos (Neume)
The custos (plural custodes , Latin for guardian ) is an auxiliary sign in the square notation of the Gregorian chant as well as in the white and sometimes black mensural notation . It can only stand at the end of the staff or before a change in the clef and shows the note with which the singing will continue. Custodes serve as a reading aid to help find the next note and are not sung or played.
Custodes are also used in performance material for baroque and classical compositions, among others in Antonio Vivaldi and Johann Sebastian Bach . Bach notates them, for example, in the autograph of his sonatas and partitas for violin solo as smaller notes with a curved neck at the end of a staff, which anticipate the first note or the first chord of the following line to make it easier to read on.
In French textbooks of the 18th century it is also called Guidon , in English Direct , in Italian Mostra , and in German Weiser .