I collected this rock slab two years ago outside Napoleon, Indiana, and didn't get around to identifying the two "rings" until this week, when I asked two members of my fossil club for their help. What we have are two specimens of cyclocystoid in the same slab. Each is about 12mm in diameter. Because I collected this from spoils piles, I can't pinpoint the period, but my guess is Silurian or Ordovician. There's no evidence of the peripheral skirt, plates or radiating lines from the center. Only the cupules. I will call on another club member to see if he can do any cleaning that might reveal more of these specimens. I'd appreciate any help you can provide regarding genus and/or species.