RILM abstract: "The basset horn came into being around 1788. Mozart used it for his concerto K.622 and quintet K.581, and for certain arias in Cosi fan tutte and La clemenza di Tito. Other works of Mozart may have been realized with the basset horn, particularly in performances by Anton Stadler."
"Reading between the (Ledger) Lines: Performing Mozart's Music for the Basset Clarinet,"
Performance Practice Review:
2, Article 3.
Available at: http://scholarship.claremont.edu/ppr/vol10/iss2/3