OK, here's the "Scientific American" version. Cephalopods, including ammonoids and actinoceratoids, are mollusks. Living cephalopods include squid, octopus, and nautilus. Extinct representatives include the lovely spiral shells of the ammonites. Early cephalopods had relatively straight shells, like long cones with chambers inside. The chambers were separated by walls ("septa") and connected by a long tube ("siphuncle"). In some groups, the shell became coiled into a flat, symmetrical spiral (e.g., modern Nautilus). The septa also became very complexly and beautifully shaped in some groups (e.g., ammonites). But in the Devonian, there were still plenty of straight, conical ("orthocone") cephalopods swimming in the sea. Oddly, some of the ammonites became UNcoiled, though they retained the complex septa. These relatively late forms are common in Cretaceous rocks and include genus Baculites. Andrew K. Rindsberg Geological Survey of Alabama