containing Mammalian Remains. 



547 



elongated lateral tooth in the right valve of the recent, is 

 much more strongly marked than in the fossil, and there is 

 a corresponding difference in the anterior lateral tooth of the 

 left valves. Several other marks of difference are to be 

 observed in the forms of the hinge teeth. 



Valvata. 



Fossil Valvata from Grays, Essex ; magnified. 



It appears that two recent species are commonly con- 

 founded under the name of Valvata piscinalis. This fossil 

 differs from both in several particulars which I have pointed 

 out in the following table, in which I have designated the 

 fossil species as No. 1, the larger recent species as No. 2, 

 and the smaller recent species as No. 3. 



COMPARATIVE VIEW OF THE THREE VALVATM. 



Unio. 



The recent Unio, which approaches most nearly to this 

 fossil, is the Unio littoralis of Draparnaud, which I have re- 

 ceived from Auvergne. The approximation is certainly very 

 close, nevertheless there are a few points of difference, which 

 I will proceed to notice. In the first place, the posterior 

 extremity is much more aslope in the U littoralis than in 

 the fossil ; then the anterior muscular impression is wider, 

 the lateral teeth are shorter, and the cardinal teeth are more 

 prominent in the recent than in the fossil shell. The form 

 and direction of the cardinal teeth and of the anterior slope 

 are also different ; the above are the most obvious marks of 

 difference that are at present observable ; it should, however, 



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