Made by Louis C. Knackstedt, these lovely celluloid mandolin picks are dated (and patented) Nov 10 1914. They are hand-bevelled and contain three semi-vulcanised rubber plugs. This ensures that it is softer on the thumb and fingers.
Louis C. Knackstedt was a bit of an inventor and also invented a support for 'eyeglasses and eyeshades' in 1922! As far as I know, he lived in Annapolis, Maryland and may have been married to an Alice Anita Switzer.
To view the original patent click below. It contains some lovely diagrams and explains the design in full.