Protocycloceratidae

The Protocycloceratidae comprises a family of ellesmerocerids from the lower Ordovician characterized by long, straight or slightly curved shells that have transverse ridges, or rings. Siphuncles are marginal or submarginal, 0.1 to 0.3 the shell diameter. Septal necks are short, orthochoanitic (i.e. straight). Connecting rings in some are thin and homogeneous, in others thick and layered.