Pterotocrinus rugosus Onychocrinus sp. Pentremites sp. Mississippian Indian Springs Shale Sulphur, Indiana Size: 24 cm across the plate. This is a plate from the famous Sulphur road cut. It has two specimens of the crinoid Pterotocrinus and the crinoid Onychocrinus as well as several specimens of the blastoid Pentremites, three of which have brachiols. Click on image to enlarge.