ABSTRACT: Between Lithuanian and Latvian there are considerable differences with regard to the derivational structure of substantives (especially in the categories of nomina actionis, nomina collectiva and diminutives). A number of derivational isoglosses link the Lithuanian language to Old Prussian and oppose it to Latvian: nomina collectiva in *-ī-no-, *-ā-to-; diminutives in *-ol-Ìo-, *-i-s-t-Ìo-; nomina agentis in *-i-ko-; nomina attributiva in *-in-ī-ko-, *-e-no-, *-āt-Ìo-, *-ōl-Ìo-; nomina qualitatis in *-ībē, *-ī-s-tā, *-is-ko-. Some of these might reflect the influence of Western Baltic upon the formation of the Lithuanian language (especially upon its western and southern dialects). The main exclusive derivational innovation in...