Rule §13
Class VII takes prefix tu— in the singular and matu— in the plural, and is very rare; many words that begin with tu— instead have that syllable as part of the root and belong to class IX (e.g. tulu 'chest', pl. jitulu).
Chatelain’s original wording (1889)
A cl. VII tem no sing. o pref. tu—, e no pl. matu—. São rarissimos os nomes d'esta classe. Em muitos nomes que começam por tu—, esta syllaba faz parte do radical. e esses nomes pertencem à cl. IX. Ex.: tulu, peito, pl. jitulu.