This is the Simplex 303 Tourist with its distinctive mounting arm that is designed to allow you to swing it out of the way when you remove the rear wheel. I have never yet seen a production version with a black mounting arm and riveted on name plate as appears to be shown here.

• Publisher: L’Institut national de la propriété industrielle
• Inventor: Lucien Juy
• Country: France
• Date: French application January 1955
• Derailleur brands: Simplex
• Derailleurs: Simplex 303 Tourist