This fossil is much sought after because it is quite rare to find. It is a sponge fossil called Brachiospongia tuberculata. The fossil dates to the Ordovician Period. The genus was originally described by Marsh in 1867 in the American Journal of Science and Arts. A different species was described by Henry Nettelroth(1835-1887) in his 1889 Fossils of the Silurian and Devonian Rocks.
On display at Cincinnati Museum Center as of August 2013. It is labeled a type specimen and apparently found in July 1879.
Learn more at UGA Stratigraphy Lab web site.
