What is "trombonium"

The trombonium is an instrument formerly manufactured by H.N. White Company and Conn-Selmer. It was unveiled by H.N. White in 1938 and was manufactured until the mid 1970s. The trombonium has the same tone of a regular trombone, except in a smaller, more compact form. It was originally designed to be used as a marching trombone. It was used by the University of Southern California Marching Band.