A lovely example of the nautilus, Cératite Nodosus, from Shell Lime Superior deposits near Alsace in northeastern France on the Rhine River plain. Ammonite and nautilus shells are made up predominantly of calcium carbonate in the form of aragonite and proteinaceous organic matrix or conchiolin arranged in layers: a thin outer prismatic layer, a nacreous layer and an inner lining of prismatic habitat. While their outer shells are generally aragonite, aptychus are distinct as they are composed of calcite.
The aptychus we see here, hard anatomical structures or curved shelly plates now understood to be part of the body of an ammonite or nautilus, are often referred to as beaks. If you look closely at this specimen, you can see the beak of the nautilus, that wee pointed piece, near the centre. Collection of Ange Mirabet, Strasbourg, France.
