Penzel Muller & Pruefer Co.
This is a Penzel Muller & Pruefer Co. Albert system clarinet.
The interesting thing about this example is the side register key. Typically, register keys are either wrapped around entirely to the front of the instrument or stay on the back. This one is off to the side, a strange feature in an albert system clarinet, especially.
Clarinet currently resides in the collection of David Watson of California.