LIFE ON THE EARTH. 75 



between the Caradoc and Wenlock formations, and 

 receives from him the name of Llandoveiy Rocks. 

 Hardly a single genus (Mdulites may perhaps be 

 one exception), but as many as 71 out of 193 species 

 seem to have been found exclusively in these deposits. 



Plants. Fucoids. 



Amorphozoa 2 genera 2 species. 



Zoophyta 14 26 



Echinodermata 5 6 



Annelida 2 3 ,, 



Crustacea 11 16 



Polyzoa 3 5 



Brachiopoda ... 13 69 



Monomyaria ... 2 5 



Dimyaria 8 13 



Gasteropoda ... 13 26 



Heteropoda ... 1 6 ,, 



Pteropoda 3 3 



Cephalopoda ... 5 13 



We find in the Upper Silurian Strata the system 

 of life unequally represented in the different parts 

 of the series, most full in the Wenlock and Ludlow 

 groups, and reduced almost to nothing in the upper- 

 most beds. In the Wenlock group, which contains 

 the principal calcareous mass of the Silurian Strata, 

 we find : 



Amorphozoa ... 3 genera 3 species. 



Zoophyta 29 66 



