This appears to be one of the early ‘cog driven’ Westminster designs. Interesting spelling of ‘Wesminster’ - and I am not entirely clear what is ‘Anglais’ about this derailleur - it seems pretty French to my untrained eye.

• Publisher: L’Institut national de la propriété industrielle
• Inventor: Jean Lionard and Pierre Champin
• Country: France
• Date: French application April 1935
• Derailleur brands: Lionaxe
• Derailleurs: Lionaxe Westminster