Article: A Silurian cephalopod genus with a reinforced frilled shell

A new cephalopod genus, Torquatoceras, comprising two new species T. undulatum and T. auritum, is described from the Silurian of Gotland. Torquatoceras is unique in that transverse crenulated frills have been secreted during the entire growth of the shell. These frills, mainly consisting of prismatic layers, might have served as a reinforcement of the shell. In T. undulatum sexual dimorphism based on size variations is demonstrated. In T. auritum there are two vertical septa inside the body-chamber, partly separating the hyponomic sinus from the apertural opening.