Below are some strange floating crinoid fossils that were given to me by my friend Herb. I believe they are dorsal cups from a Agassizocrinus laevis as they seem to match the picture and description given in "Index Fossils of N. America", Shimer and Shrock, M.I.T. press, 1944 (pg 175-176, pl.61). The description of these crinoids indicates that the plates of the dorsal cup were fused in adult specimens but juvenile specimens might still show some detail as well as a stem attachment point.
Top surface where the arms would have attached
Specimen 2. Top surface where the arms would have attached
These fossils came from Chesterian aged rocks near Leitchfield, Kentucky. Chesterian is an old North American stage name for rocks that are classified by the ICS as being in the late middle to upper Mississippian Epoch (upper Visean to Serpukhovian stage).
After talking with Herb he confirmed that they came from the Ste. Genevieve formation. Thank you Herb for giving me these fossils!