74 LIFE ON THE EARTH. 



Annelida 6 genera 8 species. 



Crustacea 28 82* 



Polyzoa 9 27 



Brachiopoda ... 12 67 



Monomyaria ... 2 ,, 7 



Dimyaria 10 31 



Gasteropoda ... 10 25 ,, 



Heteropoda 1 7 ,, 



Pteropoda 4 ,, 7 



Cephalopoda ... 4 ,, 26 



Two new classes, Amorphozoa and Echinodermata, 

 appear among the lower groups of the Invertebrata. 

 Crustacea ascend to a great predominance, both in 

 number, variety, and magnitude, still belonging to 

 the same divisions; Cephalopoda, Gasteropoda and 

 Dimyaria grow to be numerous. Thus the aspect of 

 the marine Fauna is greatly altered. 



Brachiopoda abound, and now Rhynchonella, an 

 existing genus, appears, but without Terebratula, 

 which is also living. Among the Dimyaria, Pleuro- 

 rhynchus is recorded, but Arcadse and Mytilidse are 

 the predominant races, Aviculidse still the only Mo- 

 nomyarian group. Among the Gasteropoda Murchi- 

 sonia prevails. Orthoceras, comparatively rare in 

 Llandeilo rocks, is here abundant. Star-fishes appear 

 among Echinodermata. 



The series of strata next above is regarded by 

 Murchison as a transitional or intermediate group 



