Macrobius, On the Dream of Scipio 1.14.20 (Critolaus, fr. 18 Wehrli 1969b)

Critolaus the Peripatetic [teaches] that [the soul] is constituted of the fifth substance.

Tertullian, On the Soul 5.2 (Critolaus, fr. 17 Wehrli 1969b)

Nor do I speak only of those who fashion [the soul] from things that are clearly corporeal, as Hipparchus and Heraclitus do from fire, Hippo and Thales from water, Empedocles and Critias from blood, Epicurus from atoms (if atoms too produce corporeities from their coming-together), as Critolaus and his Peripatetics do from some fifth substance (if it too is a body, since it includes bodies), but I adduce also the Stoics, who call the soul spirit, virtually [agreeing] with us, in that breath and spirit are very close to each other, but nevertheless will easily persuade [us] that the soul is body.