Again, the spines arising from the basal crust of ??'
It is almost made up of fragments of spines, teeth and scales of ganoid fish.
Sp, Anchoring spines of the statoblast.
Among the ammonites the loss of power to coil the shell is one feature of racial old age, and in others old age is accompanied by closer coiling and loss of surface ornamentation, such as spines, ribs, spirals; while in other forms an arresting of variability precedes extinction.
The skin is devoid of ossifications, but large and numerous cutaneous spines are often present, especially on the head and on the tail.