IanC:"The symphonium doesn't use the concertinal keyboard note layout. It's much simpler. Tere are some photos somewhere on the web".

RE:Not correct I'm afraid.The patent claims are 1) the "employment of two parallel rows..." ( for the diatonic notes) and 2) "the introduction of two additional rows.." (for the semitones)
In all the complete keyboard we know as the "English". it is noteworthy that the patent figure 25 includes a set up of the complete 4 row keyboard in the key of Eb prooving that the keyboard "design" was NOT ( as is sometimes assumed)based on the idea using the doublings of D#/Eb and G#/Ab to enable mean tone temperament tuning.
Add: there are 4 more patent claims as well...

TheSnail:"It is essentially a diatonic English system without the "black notes" of the outer rows".

RE: Same answer as to IanC...do check the original papers, they are very interesting, as well as the 1844 papers (also commonly misinterpreted)