https://www.chmtl.indiana.edu/hmt/thesauri/heinrich-isaac/sources/formschneider/index.html
Formschneider: Sources: Choralis Constantinus II: Digital Archives: History of Music Theory: Center...
The second volume of a three-volume set. Volume I was published in 1550 and volumes II and III in 1555.
history of musicdigital archives