The design that is being registered here is that for the derailleur protector (pare-chocs). But the document includes some nice photos of a Simplex bell-crank operated derailleur, which may be a Simplex Grand Tourisme or a Simplex Rigidex of some sort - I am too tired and confused to identify the exact model!

• Publisher: L’Institut national de la propriété industrielle
• Inventor: Lucien Juy
• Country: France
• Date: French application October 1954
• Derailleur brands: Simplex
• Derailleurs: Simplex Grand Tourisme