PART I. CHAPTER III. 



45 



Distinction of Freshwater from Marine Formations. 



Fig. 29. 



Planorbis euompkalus ; 

 Isle of Wight. 



^ Fig. 32. 



Succinea elongata ; 

 fossil. Loess, Rhine. 



Fig. 30. 



Fig. 31. 



Limnea longiscata j 

 fossil. Hants. 



Puludina lenta ; 

 fossil. Hants 



Fig. 33. 



^ncylus elegans ; 

 fossil. Hants. 



Fig. 34. Fig. 35. 



Valvata ; Physa 

 fossil. hypnorum, 

 Grays, Essex. recent. 



Fig. 36. 



Fig. 37. 



Fig. 38. 



Fig. 39. 



Auricula ; 

 recent. Ava. 



Physa colum- 

 naris. Paris 

 Basin. 



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 genns, it being scarcely possible 



Fig. 40. Fig. 41. 



J\reritina globulus. Paris basin, J\rerita granulosa. Paris basin. 



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



