74 THE OPEN BOOK OF NATURE 
inky water. Naturally only the hard parts of such 
Cephalopods are preserved in fossil form. This class 
of animal was far more abundant in former geological 
periods than it is now. Many of the extinct kinds 
possessed shells, so that fossil remains are numerous, 
—= thy, 
LSS j 
= —————— 
Clymenia striata Nautilus cariniferus 
(Devonian). (Carboniferous). 
PURER, A>’ 
a a 
Ammonites communis (Jurassic). Ammonites Jason (Jurassic). 
Fie. 23.—Somr Fosstn. CEPHALOPODS. 
It would seem that in very early times the Cephalo- 
pods were the masters of the sea. Like the rest of 
the Mollusca, their fossils range from Cambrian 
times, but they are not well represented in the strata 
of that Period. They appear in increasing numbers 
and forms in Silurian, Devonian, and Carboniferous 
