This horn coral was known by several other names: Amplexus yandelli Rominger 1876 and Blothrophyllum zaphrentiforme Davis 1887. E.C. Stumm describes it in Silurian and Devonian Corals of the Falls of the Ohio on page 50, "Coralla simple; subcylindrical to narrowly ceratoid with typical rejuvenation seen where epitheca has been removed. Calyx with steeply sloping walls. Septa 60-74; major extending almost to axis and probably amplexoid; minor short peripheral ridges."
See Plate 102 of the Blothrophyllum zaphrentiforme figures 8-15 in Kentucky Fossil Corals A Monograph of the Fossil Corals of the Silurian and Devonian Rocks of Kentucky by William J. Davis.
It lived in the Middle Devonian Period (397-385 million years ago) in a shallow tropical sea that covered the area of Jefferson County. Also see this image at the Indiana Memories Database.
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