While searching an exposure of the Keyser formation near Mt. Union, PA I found some odd rounded objects.
I think they may be Cystoids but when I found them they had no discernible markings. Thinking them to be chert nodules I soaked them overnight in some vinegar and that is why they look a little etched. It wasn't until I got a closer look at the etched pieces that I noticed what looked like a pattern of plates. You can see what I am talking about in the specimen below.
As you can tell from the pictures above it seems to have a diamond shaped cross section so maybe that represents a top and bottom. I do not see any clear evidence of a stem or arms though. At this point it looks like the pattern may be an internal mold of a Cystoid or Crinoid but I doubt I'll ever be able to ID it since there it little to go on.
The Keyser formation is upper Silurian to lower Devonian in age (Pridolian to Lochkovian stage).