4 
(b) Fossil — continued ; — 
Pliocene 
Miocene ... 
Oligocene ... 
Eocene 
Cretaceous ... 
Jurassic 
Triassic and Liassic 
Permian 
Carboniferous 
Devonian 
Silurian ... 
Ordovician ... 
Cambrian ... 
III. Systematic Index = 2231 ; — 
Gastropoda 
Polyplacophora ... ... 
Prosobranchia 
Opisthobranchia, including Pteropoda and Heteropoda 
Pulmonata 
Scaphopoda 
Pelecypoda or Lamellibranchia 
Cephalopoda 
Incertae Sedis ... 
PAGE 
S26 
. 26 
. 26 
. 27 
. 44 
. 45 
. 52 
. 52 
. 60 
. 61 
