This is a 1928 Conn F Mezzo-soprano saxophone, freshly overhauled by me.
These saxophones in the unusual key of F were introduced months before the market crash of 1928, and only a few were sold- to those rare customers who were both saxophone crazy and had disposable income during the Great Depression. The unsold horns- which were the majority- were used as fodder at the Conn repair school. As a result, not many of these unique instruments survive, and even fewer still in this condition.
Behold a beautiful survivor, an orphan of the Jazz Age.
(click for high-resolution photos)
And here is a size comparison, next to a regular Eb alto (also a Conn, in this case a 1932, but not yet overhauled):
For more information on the Conn F Mezzo-soprano saxophone, see here:
1. The Saga of the F saxophone, by Paul Cohen (pdf)
As of 9-13-2012, this horn is available for sale here: Getasax.com: Conn F Mezzo-soprano
I made a Repairman’s Overview of this horn as well: