156 



INVERTEBRATA. 



1 



phosphatised, and the outer whorls have usually been worn by 

 attrition, so that fair-looking specimens can only be obtained by 

 breaking away the outer whorls. Many of the shells have been 

 utterly broken up and rolled into pebbles. 



A broad-whorled, many-ribbed variety of this species al 

 occurs in excellent preservation at Brickhill, Upware, and Potton 



From their occurrence with Astarte cuneata, Trigonia incurva 

 and other fossils of Portlandian and Purbeck age, and from the 

 nature of the phosphate in other specimens, I conclude that most 

 of these Ammonites were derived from old Portlandian and Pu 

 beck rocks.but others were I believe gathered from the Kimmerid 

 Clay, whilst some few are of Oxfordian types. 



3n 



I 



Ammonites biplex, d'Orb., non Sby. 



A well-marked Oxford Clay form with narrow whorls anij 

 depressed bands, or varices running at intervals around thei 

 This species, as also Ammonites cordatus, var. Lamherti, and A'i 

 monites cordatus, var. Marice — all of them from the Oxford Clai 

 invariably occurs mineralized in oxide and sulphide of iron. 



The remains of Gasteropod shells are rather numerous, but 

 they are much worn, and but few of them can be specifically iden- 

 tified. We recognise the following : 



Chemnitzia Heddingtonensis, Sby. Nerincea. 

 Alaria. Several species. 

 Cerithium muricatam, Sby. (from 

 the Coral Rag). 



Other Jurassic species are : 

 Lamellihranchiata : 

 Ostrea gregaria, Sby. 

 Pectunculus, sp. 

 Cardium striatulu?n, Sby. 1 

 Lucina Portlandica, Sby. 

 Trigonia gibbosa, Sby. 

 „ incurva, Sby. 

 Astarte cuneata, Sby. 



„ Hartwelliensis, Sby. 



Echinodermata : 



Ajnocrini/s ? column of. 



Pleurotomaria reticulata, Sby. 

 Natica. Several species. 



Cyrena rugosa, Sow. 

 Myoconcha Portlandica, Blake. 

 Myacites cuneata, Phill. 



,, parallellus, Phill. 

 Pholadomya tumida, Ag. 

 Pholadidea (Kimmeridge clay sj 

 cies). 



