Duccius[?] - inscriptions, notably a tombstone of Lucius Duccius Rufinus at York[2] (http://museums.ncl.ac.uk/archive/arma/contents/iconog/tombston/cent1/uk/york/duccius.htm)
... middle and passive is not maintained in later Sanskrit). The four systems are:
Present[?] (Present[?], Imperfect[?], Imperative, Potential)
Future (Future[?], ...