This sounds like a very rare find indeed but it is unfortunate that the
works are missing.  It is possibly a Diamonion, but under a different
name.

Around 1900 to 1903 Paul Ehrlich manufactured an upright disc playing
cabinet piano.  This appears in an advert reproduced on page 267 of
Clockwork Music, by Arthur Ord-Hume.  The instrument appears to play
the Ehrlich 36-note cardboard disc, otherwise used on the 36-note Ariston
organette and the Hupfeld Piano Playing Mechanism No. 10, which was
made by Ehrlich.  This disc is 420 mm in diameter, which fits with the
approximate diameter given by Mike Moran.

The picture shows the disc driving hub at mid height on the front of
the instrument with two doors, one above and one below.  The mechanical
keyframe is horizontal and to the right of centre.  The top door is
shown missing and inside there appears to be a vertically strung piano
mechanism.

A handle is seen on the right hand side of the case.  It is unclear
whether this is a clockwork or hand cranked instrument, although as
Mike's has a coin slot this would imply that there was a clockwork
motor.

Photos of the empty case will help further identification.  To date,
there is no known example of the Diamonion in existence.

The Diamonion must have had a very limited appeal as by this time
pneumatic pianos were becoming more sophisticated and able to give more
life-like performances.  Disc played mechanical pianos have limited
expression, if at all, and give a jerky performance.  They do,
however, make interesting museum pieces.

Best regards,
Nicholas Simons, UK