Full Plateau Unibody Buffet A Clarinet with Donut Key

Here is an interesting piece.

This Buffet Crampon A clarinet is a unibody, featuring full plateau keys with one "Donut" key.  
The donut key was somewhat popular among Buffet products (see Buffet G Fischer and Buffet Antique Unibody pages) during the early 20th century.
However, this appears to date even earlier, from around 1860-1890, making this quite an early example of Boehm keywork.
Better yet, it features an articulated C#/G# key.