100 



wear, they cannot be relied upon for discrimination ; the 

 want of the spiral ridge in the umbilicus, is the most con- 

 spicuous character, aiul is constant. 



Lent me from Barton by Miss Dent. It occurs also 

 in France, but I do not know that it has been described. 

 Were it not for the constant absence of the lesser spiral 

 ridge in this, and its regular appearance in all the speci- 

 mens of the Crag species, they might have been con- 

 sidered as varieties, but this character is so closely con- 

 nected with that of the Genus, that it must surely be of 

 importance enough to distinguish a species. 



