loG INVERTEBRATA. 



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 also 

 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 Pur- 

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

 Clay, whilst some few are of Oxfordian types. 



AMMONITES BIPLEX, d'Orb., non Sby. 



A well-marked Oxford Clay form with narrow whorls and 

 depressed bands, or varices running at intervals around them. 

 This species, as also Ammonites cordatus, var. Lamberti, and Am- 

 monites cordatus, var. MaricK all of them from the Oxford Clay, 

 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. 



Alarla. Several species. Pleurotomaria reticulata, Sby. 



Cerithium muricatam, Sby. (from Natica. Several species, 

 the Coral Rag). 



Other Jurassic species are : 

 Lamellibranchiata : 



Ostrea gregaria, Sby. Cyrena rugosa, Sow. 



Pectunculus, sp. Myoconcha Portlandica, Blake. 



Cardium striatulum, Sby. ? Myacites cuneata, Phill. 

 Lucina, Portlandica, Sby. paralleling, Phill. 



Trigonia gibbosa, Sby. Pholadomya tumida, Ag. 



incurva, Sby. Pholadidea (Kimmeridge clay spe- 

 Astarte cuneata, Sby. cies). 



ffartwelliensis, Sby. 



Ecldnodermata : 



Apiocrimu ? column of. 



