78 



LIFE ON THE EARTH. 



poda, but difference of time is marked by Gastero- 

 poda and Fishes. 



From the data thus collected we may compile 

 one general table representing the numerical preva- 

 lence in time of each of the classes of Marine Inver- 

 tebrata in the Lower Palaeozoic Strata as at present 

 known. 



By inspection of this table it appears that the 

 earliest system of marine life contained a few exam- 

 ples of five great classes; viz. Zoophyta, Annelida, 

 Crustacea, Polyzoa, Brachiopoda. 



In the next period all the ordinary classes of 

 Mollusca are added, in small numbers. 



In the third period, Echinodermata appear, and 

 perhaps Amorphozoa, for this seems, to me at least, 

 still somewhat doubtful. 



Thus excepting Cirripedia which up to this time 



