Somewhat rare brachiopod fossil found in the Silurian Louisville Limestone which is known more for its corals. This fossil appears to some sort of Pentamerus but after some research it might be a Rhipidium knappi named by Hall and Whitfield. The Index Fossils of North America names it being found in Kentucky (Louisville Limestone) and west Tennessee (Brownsport). Might also be under the name Hall gave in in 1872 as Pentamerus knappi or his 1875 identification Pentamerus nysius var. crassicostus.
See images of it in the Henry Nettelroth (1835-1887) book on Kentucky Fossil Shells (1889): CLICK HERE
