A man from Hennepin, IL found this while digging in his yard. I took several photos, (although, I neglected to get a close-up shot). It seems unlikely that it was transported by the Illinois River; it may have been placed in the yard by a previous owner.
The fossil is slightly less than 1 foot across. This is what I think is the top. It is slightly dome-shaped and layered. The small spots appear to be colonial. (It looks like a coral or a recipticulid.) There is sediment between the layers.
IDENTIFIED!!!: Joe Devera and Russ jacobsen of the ISGS tell me that this is a Bryozoan! The colony probably started growing on top of the dead crinoid.
Bottom (?). There is a crinoid stem embedded in the center. Note the layering.