In among the snails on the previous page are a few of these fossil Cephalopods. Think of a modern squid's body with a hard shell at the tail end.
In the photo above the head would have been pointed to the right, the tail to the left. The darker material would have been the shell, with be body stuffed inside the funnel shape. The finer lines in the funnel (lower photo) would have been the growth chambers - as the Cephalopod grew it moved forward in the shell, partitioning off the rear chambers, just as the modern Nautiloids do. The white rod is a central stiffening rod, replaced by minerals during the fossilzation process.
The hard external shell probably evolved as a defense against predators.