[M.:] Neutra quae sunt?
[D.:] Quae in -ō dēsinunt ut āctīva, sed acceptā -r litterā Latīna nōn sunt, ut stō, currō (“stor, curror” nōn dīcimus!).
Neuter verbs? I don’t see anything like that in my grammars. To what is he referring?
He seems to be referring to intransitive verbs that don’t have a 1st person singlular passive form, though without more context it’s difficult to tell.