A few weekends ago, I was able to attend a field trip to Napoleon, Indiana USA. While there, I found this fossil which appears to be a Holocystites gyrinus (Miller & Gurley, 1894) cystoid. It dates to the Silurian Period (Telychian to Sheinwoodian stage) in age. The locality is world famous for this type of fossil. This specimen should be prepped to reveal more surface texture.
According to Dr. James Thomka, professor at SUNY Plattsburgh, it is "from the mudstone lithofacies of the Massie Formation (long known as the "upper Osgood shale"), which is renowned for its 'cystoid' fauna."
