216 CONTRIBUTIONS TO GEOLOGY. 



Observations. This species was obtained from the sand 

 removed from the cavity of a large shell. In some of its 

 characters, it answers the description of the planulata (Lam- 

 arck). It differs from the saxorum of Blainville, in having 

 the lobes in contact, and in having the mouth terminal. 

 In his figure it appears to be lateral. The most striking 

 character of our species seems to be, that it possesses a 

 large tooth, which partly fills the aperture. This, I be- 

 lieve, has not been before observed in any described 

 species. 



Lamarck describes four fossil species ; three are from 

 Grignon, and one from Louvres, near Paris. It has not 

 before been observed, I believe, in this country. 



