Is it possible that "hot fountain pen" was a slang term for clarinet, similar to "licorice stick"?
Also, found this definition of a Goofus: Goofus - a kind of two-octave keyboard-mouth-organ, manufactured in France in the 20s and played by blowing directly into it, or through a length of tubing that allows the instrument to be laid flat on the stage. Adrian Rollini, who features it to great effect, favoured this method.
Just type "goofus instrument" into the Google search engine and you'll have everything you ever wanted to know about it at your fingertips!