This article provides a study of Diomedes’ treatment of verbs quae R littera finiuntur (GL I 374, 23 - 377, 20). This analysis includes two passages where Pliny’s Dubius sermo is explicitly quoted (frg. 110 and 119 Della Casa = 107 and 110 Mariotti²), but other material deriving from Pliny can reasonably be identified, thanks to quotations from non-literary authors who are explicitly used as sources for the Naturalis historia or for other works not studied in school and quoted elsewhere in the Dubius sermo. The parallels between these passages from Diomedes and those from Priscian, who explicitly draws on Caper, show that the latter was probably the intermediary through whom the learned study of grammar from the first and second centuries AD was transmitted to late Latin scholars.