While the twin pulley wheel Westminster Route is a relatively well known model, this derailleur is more obscure. It appears to be a single pulley racing version. If I was a betting man I would wager that it was called ‘Course’ - but I have no supporting evidence for that.

• Publisher: L’Institut national de la propriété industrielle
• Inventor: Jean Lionard
• Country: France
• Date: French application March 1938
• Derailleur brands: Lionaxe
• Derailleurs: Lionaxe Westminster Course?