I'm a little surprised that I hadn't posted a specimen of Tornoceras arkonense to my blog yet. It's a small cephalopod that is found only in the Arkona formation at the site where I collect at Hungry Hollow along the Ausable river in Ontario, Canada. The fossils are preserved by pyrite and can be very detailed. below is a typical specimen with views of the suture in profile and from the front.
The Arkona formation is middle Devonian (Givetian stage) in age.