326 



HELICID^. 



Arkansas, and Texas. It is the most universally distri- 

 buted of all our species. 



Remarks. This is a well-defined species, and may 

 always be known by its sub-conical shape and triangular 

 aperture, nearly filled up by the coarse, projecting, colu- 

 mellar tooth. The description here given applies to the 

 most common form of the mature shell, as ascertained 

 from the examination of more than one hundred spe- 

 cimens from difierent localities. Among a number of 

 specimens, there will of course be different degrees of 

 development and consequent variation from the normal 

 form. Specimens from particular localities seem always 

 to be more delicate, and never to attain that coarseness of 

 parts in the aperture which is common. There is some- 

 times a slight thickening of the left lip, near its extre- 

 mity. Mature specimens vary considerably in size. 

 The aperture is beautifully white within. 



