LIFE ON THE EARTH. 77 



Zoophyta 8 genera 10 species. 



Echinodermata ... 11 17 



Annelida 6 8 



Crustacea 15 39 



Polyzoa 1 1 



Brachiopoda 10 30 



Monomyaria 2 17 



Dimyaria 10 41 ,, 



Gasteropoda 10 27 



Heteropoda 1 4 



Pteropoda 3 4 



Cephalopoda 5 30 



! Fishes 5 7 



The decline of the whole series is very marked in 

 the Passage-beds, which yield only the following 

 meagre list. 



Plants probably terrestrial Lycopodiaceae ? 



Crustacea ... 5 genera 11 species. 



Brachiopoda... 1 1 



Gasteropoda... 1 1 



! Fishes 5 7 



Of the few species here noted, three Fishes, the 

 two Mollusks, and six of the Crustacea, are also 

 found in the upper Ludlow beds, of which indeed 

 these are merely the capping. This decline of the 

 Silurian species may be compared with the dawn of 

 the series in the Lingula Zone ; the analogy of con- 

 ditions is maintained by the Crustacea and Brachio- 



