DESCRIPTION OF THE PLATEvS. 



Fig. 8. The magnified spines of the preceding shell. 

 9. T. aliformis. 



10. T. rudis. 



11. T. rugosa. 



12. A calcedonic cast of a shell of the genus Trigom'a. 



13. T. sinuata. 



14. The inner surface of the flat valve of Harpax. 

 15. convex valve. 



16. A magnified view of the hinge teeth of the flat valve, 



17. convex valve. 



1 8. A magnified view of the outside of the flat valve. 



PLATE XIII. 



Fig. 1. A fossil shell of the genus Cucullaa. 



2. Crassatella tumida. 



3. A calcedonic shell resembling Cardium aoh'cum. 



4. A rostrated shell, perhaps of the genus Tettina. 



5. Cyclus deperdita, with crenulated teeth. 



6. A donax-formed fossil shell from Gloucestershire. 



7. Another fossil shell, supposed to be of this genus. 



8. Another fossil shell, apparently of this genus. 



9. The inside of Trigonellites l&ta. 



10. The inside of Trigonellites lamellosa. 

 "11. The outside of Trigonellites lamellosa. 



12. The outside of Trigonellites lata. 



13. Erycina Items, on the inside. 

 14. -, on the outside. 



15. Outside of Venericardia senilis from Essex. 



16. An uncommonly marked fossil bivalve from Bedfordshire. 



17. Inside of Venericardia senilis. 



