THE SPECIES PROBLEM WITH FOSSIL ANIMALS 



CORTES 

 1B0VIS 



EVOLUTION 

 OF 



MICRASTER 



Fig. 15. Evolution of the spatangoid echinoid genus Micraster as re- 

 corded in six zones of the Cretaceous of southern England. Some of the 

 characteristic features of the five designated successional species are in- 

 dicated by ventral and lateral profiles. I, Zone of Cyclothyris cuvieri; 2, 

 /.one oi Terebratulina lata; 3, Zone of 1 1 olastcr planus; 4, Zone of Micraster 

 cortestudinarium; 5, Zone of Micraster coranguinum; 6, Zone of Marsupites 

 testudinarius. Constructed chiefly from data given In Kermack (1954). 



