This series of pictures are of a Devonian period horn coral called Craterophyllum magnificum (Billings). I have been looking for one of these for a while since I just found a fragment a year or two ago. They were pretty large corals. This fossil measures 2 cm at base, 6 cm tall, and 8 cm wide at the top. I am guessing it would have been 8-10 cm in diameter.
Stumm's Silurian and Devonian Corals of the Falls of the Ohio says this about this coral. "The specimens from the Falls of the Ohio may not be conspecific with Billings' type, but detailed examination of Canadian material must be made before this can be determined. Hall's description of Chonophyllum capax fits this species perfectly. His Silurian age designation is apparently in error."
My cousin found this one in Jefferson County, Kentucky in the Jeffersonville Limestone.