Correspondence — T. 0. Bosicorth. 



575 



Below it there is always the Ammonites varians fauna, containing : 

 Pecten elongatus, Discoidea subiicidns, Nautilus deslongcJiampsi- 

 anus, Nautilus elegans, Turrilites, Baculites, and Actinocamax 

 lanceolatus. 



Above it is the Holaster Chalk with Cidaris BowerhanTci, Echinocyphus 

 difficilis, Holaster trecensis, Discoidea cylindrica (hemispherical 

 form), Ptychodus decurrens. 



Cambridgeshire. 



Bedfordshire 



and 



Hertfordshire. 



Oxfordshire, 



Buckinghamshire, 



and Berkshire. 



Folkestone. 



Chalk containing Cidaris Boiuerbanhi, Ptychodus decurrens, Holaster trecensis, 

 Echinocyphus difficilis, and Discoidea cylindrica (hemispherical form). 



In conclusion, I may say that the Discoideas from the Holaster 

 trecensis beds of Cambridgeshire seem to be distinguishable from 

 those in the zone of A. varians (including the Burwell Rock), but 

 I am not yet sure of being able to separate them from the large 

 forms in that zone in the south. 



^ Not listed in the General Memoir, but fairly common at Burwell. 



