PART I. CHAPTER III. 



45 



Distinction of Freshwater from Marine Formations. 



Fig. 29. 



Fig. 30. 



Fig. 31. 



Planorbis euomphalus ; 

 fossil. Isle of Wight. 



Fig. 32. 



Succinea elovgnta ; 

 fossil. Loess, Rhine. 



Fig. 36. 



Limnea longiscata ; 

 fossil. Hants. 



Paludina lento, ; 

 fossil. Hants 



Fig. 33. 



Fig. 34. Fig. a5. 



Ancylus elegans ; 

 fossil. Hants. 



Valvata ; Physa 



fossil. hypnorum, 



Grays, Essex. recent. 



Fig. 37. 



Fig. 38. 



Fig. 39. 



Auricula ; 

 recent. Ava. 



Melanopsis buc- 



cinoidea; recent. 



Asia. 



In regard to one of these, the Ancylus (Fig. 33.,) Mr. Gray 

 observes that it sometimes differs in no respect from the marine 

 Siphonaria, except in the animal. The shell, however, of the 

 Ancylus is usually thinner.* 



Some 'naturalists include Neritina (Fig. 40.) and the marine 

 Nerita (Fig. 41.) in the same genus, it being scarcely possible 

 Fig. 40. Fig. 41. 



Neritina globulus. Paris basin. Jftrita granulosa. Paris basin. 



* Gray, Phil. Trans. 1835, p. 302. 



