Don Byas and his Dolnet, Check this out!

[DanY]

I like the snake neck vent.

http://newarkwww.rutgers.edu/IJS/instrumentsB/don-byas.html

[G.M.]

Yes.Prez had one too.
One of my students has a "Royal Jazz"model,and there are all the possible keys on it,and even more!