Twenty 6 X 13 Mattey Stereoscope Cassettes

is a group of twenty (eight shown) hard rubber cassettes for 6 X 13 glass stereo views. The identification on one side reads: "Stereotheque, Brevet S.G.D.G., P.M.F. (Mason Pennard et Fouquet), Marque Depose, Stereoscope Classeur" while the other says: "IVORINE, CH. Roger, Paris, Model Depose". They fit one of the Mattey (French) mechanical changing stereoscopes. All are in very good condition but two have small pieces of the hard rubber purposefully removed which does not interfere with their function.