INTRODUCTION. 41 



19. Planorbis carinatus. 



20. corneus. 



21. vortex. 



22. contortus. 



23. imbricatus. 



24. nitidus. 



25. Bithinia tentaculata. 



26. Paludina 



27. Valvata cristata. 



28. pischialis, var. V. antiqua Morris (Loud. 



Mag. N. H., series 2., ii. 544., f. 26.). 



29. Velletia lacustris. 



30. Ancylus Jluviatilis. 



31. Cyclas cornea. 



32. Pisidium obliquum. 



33. pusillum. 



34. amnicum. 



35. Anodon cygneus. 



36. c/mo pictorum. 



All these species exactly agree with the specimens 

 of the same species now found in the neighbourhood, 

 except that some of the specimens of Valvata piscinalis 

 are much larger and higher than those usually found 

 in this country. Mr. Morris and Mr. G. B. Sowerby 

 are inclined to consider them as a distinct species, and 

 have called them Valvata antiqua ; but, on an accu- 

 rate examination and comparison of Mr. Morris's spe- 

 cimen, I believe that it is only a variety, as I have 

 seen some specimens from the warmer parts of Europe 

 which are nearly as large, and similar to these fossil 

 ones. 



Besides these 36 species, there are found with 

 them, — 



