The Discant Clausula can appear in the bass part, especially at the beginning of pieces.
One of the upper voices will have the Tenor Clausula 1-2-1 and an auxiliary voice resembling an Alto Clausula 3-4-3 (all the Alto Clausulae we’ve seen so far centered around scale degree 5, but the formal Alto Clausula is actually 5-3).
The Auxiliary voice can also take on other variants such as 3-5-3 and 3-4-5-3 (4-5 are shorter)
To add a fourth part we will add an alto Clausula with some variations to avoid parallels.