The Orthoceras is a marine cephalopod, a mollusc which had the same lineage as the modern day cuttlefish. In appearance very similar to the modern day squid, the extinct Orthoceras had a hard exoskeleton or shell defined with fine lines termed lira, these lirae covered the shell, a siphuncle which was a transversely situated tube joining each chamber of the phragmocone or shell, which acted as a system of jet propulsion much like a modern day squid filling with either gas or seawater to aid buoyancy or diving into the depths. As the Orthoceras grew it developed larger and larger chambers which can be seen in the fossilised remains within the limestone here. The limestone which was once the prehistoric sea bed millions of years ago. This Orthoceras Phragmocone is of the Palaeozoic from the Devonian era, dating back to approximately 417,000,000 to 354,000,000 years.. Located near the town of Tazzerine, the Western Sahara, Morocco, North Africa.