340 



HELICID^. 



bave specimens from JMississippi. It is probably a widely 

 spread species, although less common than some others. 



Remarks. This is a very thin and delicate shell, 

 and has a peculiar transparency, resembling spermaceti. 

 The aperture is somewhat circular, the upper part being 

 interrupted by the last whorl, and the extremities of the 

 lip not being connected. The smaller tooth is often 

 wanting, and sometimes both. In the number and posi- 

 tion of the teeth, it somewhat resembles P. exigua ; but 

 it is less fusiform, and more cylindrical. In general 

 outline, and in the shape of the aperture, it very much 

 resembles P. rupicola, but the parts within the aperture 

 are very different. It is, however, just what the imma- 

 ture shell of that species might be supposed to be, when 

 the dentiform deposits were only commenced, and the lip 

 thin and unfinished. I am much inclined to believe that 

 it is only a young shell. In the great number of speci- 

 mens which I possess, the teeth are only rudimentary. 



