I don’t think this bookplate is on any of the lists of Ritter’s work. No date or number, but it is signed by him. It may be quite a late bookplate, from the 1950s when Ritter was in Argentina. Because it might belong to this guy: Poet and Musicologist, he moved to Argentina after the war I think. His son became a bigshot music professor. I suspect that Johannes was a violinist. He translated Julio Sanchez Gardel's play The Witches Mountain into German.