Monocyrtoceras
Monocyrtoceras is a genus of armenoceratids from the Middle Silurian of North America, with a gently curved shell and a siphuncle like that of Elrodoceras.
According to Teichert, 1964, in the Treatise on [Invertebrate Paleontology|Treatise] part K, Monocyrtoceras along with Elrodoceras and Armenoceras forms one of the two branches of the Armenoceratidae.