(fl c1300). French or Spanish theorist. He may have been one of the ‘cantores de Navernia’ mentioned by Admetus de Aureliana. Admetus and Jacobus are known only from citations by Robert de Handlo in his treatise of 1326 (CoussemakerS, i, 397–8, 400–01; ed. P. Lefferts, Lincoln, NE, 1991). Jacobus distinguished three kinds of hocket, each respectively using smaller note values and rests, a typology similar to that of Walter Odington.