Given your description:  I think the discs are either a Stella (in
which case there would be only holes in the disc and no "tabs" left
from the punching of the disc or a 15" Mira, in which case the discs
will have "tabs" resulting from the punching of the disc.   If you
see a cross printed on the disc (usually under the title) over which
the letter "s" is superimposed, the disc  it is definitely one of the
two aforementioned products manufactured by Mermod Freres.  As to
value, it would be decided by the demand of the collector -- both
sizes of either the Stella or the Mira are not as common as the 17"
Stella or the 18" Mira.  A good contact for you might be Barry
Johnson in Mountain View, California (415-964-0685):  he makes new
discs of both of these types and may be interested or know of someone
who is.  Hope this helps.

Jack