70 THE DOCTRINE OF DESCENT. 



which they have in common with several of the crabs 

 now inhabiting shallow waters and coasts, and likewise 

 their general habit, allow us to infer that they also were 

 denizens of coasts. 



The Molluscs were mainly represented by Brachiopoda 

 and Cephalopoda. However, as Bivalves and Caster- 



opoda were also in existence, the appearance of this, the 

 most ancient molluscous fauna known, differs from the 

 present one only in its numerical proportions, and in the 



