Or a freak experiment gone awry.
You wrote:Where in the world did you come up
with 15.5" for this shell - you must be using a different ruler than mine.
DanShell
 
I believe that the measurement taken must be 155mm or 15.5cm  for the
gloriamaris. This would be a nice size but not too extraordinary. As for
15.5" this is impossible unless it's a new species in that case if the
conus are becoming that large I'm not going near the water again. Mark