Dear Thomas et al,
  I have looked at the scallop on your web page and do not know whether it is
my server or the quality of the photo that was scanned, but the picture is
coming through very darkly. If you can scan a lighter photo I will try to
help. But let me describe islandicus to you a little better and perhaps you
can determine yourself if it is just a variation.
  I thought I saw some shagreen microsculpture on the shell. Chlamys
islandicus has on the left valve, the brightly colored one, shagreen
microsculpture over the whole valve including the ribs. On the right valve,
the shagreen microsculpture is present in the interspaces but not on the top
of the ribs.
  Shagreen microsculpture can be described as looking like a window screen
has been placed over the shell and is absent in scraped or badly worn shells.
(If you have September 1995 American Conchologist, there is a photo of
shagreen microsculpture on p. 6)
  Another feature of islandicus is the way the ribs are formed. The ribs in
islandicus, are formed by branching. A rib will start and split and each rib
will split and split again as the shell grows. It may be possible that in
your shell the ribs just haven't split as they should have.
  Check for this. If there is no shagreen and the shell is in good shape, it
is not islandicus. If there is shagreen we can move on from there.
  After you do this, check back with me and we can try to figure it out.
        Carole Marshall