Here is a button coral called Hadrophyllum orbignyi from the Devonian Period. It was found in Clark County, Indiana. It is about the size of an American dime.
It appears this fossil was named after Alcide d'Orbigny, the French naturalist from the early to mid 1800s. While young he studied marine creatures under the microscope called foraminiferans. In 1840, he described fossils in France in a book called La Paleontologie Francaise. Oddly, Wikipedia does not list this fossil as one of the species named in his honor (checked 03/8/2009).