https://en.wikipedia.org/wiki/Trombonium:

The trombonium is a brass instrument formerly manufactured by H.N. White Company and Conn-Selmer.[1][2] It was unveiled by H.N. White in 1938 and was manufactured until the mid 1970s.[1] The trombonium has the same timbre as a regular trombone except in a smaller, more compact form.[1] It was originally designed to be used as a marching trombone, and has valves rather than a slide thus superficially resembles a tenor horn or euphonium.[1] It was used by the University of Southern California Marching Band[1] and on a handful of jazz recordings (e.g., Jay and Kai + 6).