Offered here is a neat association between the Calceocrinid Halysiocrinus tunicatus and the cladid Cyathocrinites iowensis. This piece comes from the Edwardsville formation of Monroe County, Indiana. The Halysiocrinus crown measures in at 2.5 inches long and the Cyathocrinites measures in at 1.5 inches long.

Halysiocrinus is an interesting crinoid as it is the last of the Calceocrinids, a distinct group of crinoids which goes all the way back to the Ordovician period.