Clarkesvillia is a genus of Upper Ordovician westonocerids that differs from Faberoceras in having a more flattened venter and from the later Glyptodendron in having a more ventrally located siphuncle.
References
Teichert, C. 1964. Nautiloidea -Discosorida. Treatise on Invertebrate Paleontology Part K Teichert and Moore, eds. Clarkesvillia-Paleobiology DB