Fig. 325. Slab of Rock covered with Ammonites,—a Bit of a Mesozoic Sea Bottom
Fig. 326. Representative Species of Different Families of Ammonites
The ammonite stem branched into a most luxuriant variety of forms. The typical form was closely coiled like a nautilus ([Fig. 325]). In others ([Fig. 326]) the coil was more or less open, or even erected into a spiral. Some were hook-shaped, and there were members of the order in which the shell was straight, and yet retained all the internal structures of its kind. At the end of the Mesozoic the entire tribe of ammonites became extinct.