100 
wear, they cannot foe relied upon for discrimination ; the 
want of the spiral ridge in the umbilicus, is the most con- 
spicuous character, and 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 Yarieties, 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. 
