This fossil appears to be an Arachnophyllum coral from the Silurian Period. It was found in the Louisville Limestone of Jefferson County, Kentucky. This specimen has some really good sections showing septa definition.
Here is an Aulopora precius? coral growing on the Arachnophyllum coral.
Below is the fossil with a ruler showing the fossil to be about 10 cm long.
Thanks to my cousin for loaning me this fossil to photograph!