344 ZONES OF THE CHALK. 



" The Middle Chalk may be taken to include the greater part of that formerly known 

 as the Lower Chalk, and will answer to the French Turonian. Its fauna is very different 

 from that of the beds below, most of the Cenomanian species having died out during the 

 interval marked by the formation of tlie Melbourn Rock, while other new species were 

 introduced, the chief of these being Ammonites twdosoides, Am. peramplus, Inoceramus 

 mytiloides, Rh^/nchonella Cuvieri, EcMnoconus suhroiundus, Cypliosoma simplex, Cardiaster 

 pygmiBus, and Holaster planus. 



" The Upper Chalk may be regarded as equivalent to the Senonian of the French. 

 It is characterised by the abundance of 3Iicraster coranffiiinum , Cidaris sceptrifera, Tere- 

 bratula carnea, Lima Hoperi, and in the higher zones by Marsupites ornatus, EcJiinoco7iu& 

 conicus and Belemnitella mucronata.^'' 



