An identifying feature of the Placenticeras Intercalare are the raised tubercles that are evenly spaced in two concentric rings along the spiral from the protoconch out to the edge of the living chamber. The peaked ridges along the ventral edge are called crenulations. All these bumps or spines served an ornamental as well as defensive purpose for the animal. The raised nipples on many specimens show a remarkable three-dimensional rainbow effect, changing color from every angle.
The Placenticeras Intercalare is believed by many researchers to have been the male of the species and while usually smaller, brighter and more colorful than the female - Placenticeras Meeki - it is also much less common. It is thought that the female may have displayed spawning behavior; giving birth in groups and dying immeadiately afterword thereby leaving localized graveyards of female (meeki) fossils for us to find. The male (intercalare) must have lived a solitary life as it is usually found by itself in a lonely shale tomb.