Halloceras
Halloceras is a gyroconic rutoceratid from the Lower Devonian of North America, with a subtriangular whorl section, narrow dorsum, divergent flanks, and broad, rounded venter, frills at various growth points, suture with shallow ventral and lateral lobes, and a small siphuncle near the venter.
Halloceras was named by Hyatt in 1884. The type us Halloceras undulatum.