52 HELICIM;. 



Genus III. ZONITES. 



The identification of the different species in this 

 genus gives more trouble to the novice to whom they 

 all look pretty much alike than all the rest of British 

 land and freshwater shells put together, with the ex- 

 ception of the minute Vertigos. When the adults of 

 two species differ considerably in size, as radiatulus 

 and nitidus, and the markings and sculpture are much 

 alike, it is a good plan to count the whorls of a small 

 specimen. A full-sized radiatulus has four and a half, 

 and nitidus five. If, therefore, the shell under con- 

 sideration is the size of radiatulus, and has three whorls, 

 the observer will know that another whorl and a half 

 would make the shell too large for a radiatulus, and he 

 may conclude it to be a young nitidus. 



The animals should be carefully compared. Of the 

 ten species, fulvus, crystallinus, purus, radiatulus, and 

 excavatus are unmistakable when their striking diffe- 

 rences have been once pointed out. 



1. Z. CELLARIUS (inhabiting cellars). 

 Compressed, glossy, semi-transparent, pale horn- colour 

 above, opaque white below ; spire nearly flat ; mouth deeply 

 semi-lunar; whorls five to six; umbilicus broad and deep; 

 diameter half an inch. 



