This is a Fossil of a Horn Coral from Ohio. This piece measures approx. 91  x 53 mm: thickness is approx. 28 mm: weight is 168 grams.
 
Horn Corals are from the extinct order of corals called Rugosa. Rugose means wrinkled. The outside of these corals has a wrinkled appearance. Solitary rugose corals are colloquially called “horn” corals because their skeletons were shaped like a cow’s horn.