4 
(b) Fossil — continued : — 
Jurassic 
Triassic and Liassic 
Permian 
Carboniferous 
Devonian 
Silurian 
Ordovician ... 
Cambrian ... 
HI. Systematic Index = 2231 
Gastropoda 
Polyplacophora 
Pro3obranchia 
Opisthobranchia, including Pteropoda and Heteropoda 
Pulmonata ... 
Scaphopoda ... ... ... 
Pelecypoda or Lamellibranchia 
Cephalopoda 
PAGE 
>25 
. 25 
. 25 
. 26 
. 38 
. 39 
. 45 
. 45 
. 52 
