114 UNIVALVES. 



aperture simi-lunar ; columellar lip, truncated, 

 flattish, straight, and oblique to the axis of the 

 shell. 



OBSERVATIONS ON THE SHELL AND ITS 

 INHABITANT. 



There is no genus more easily distinguished 

 than that of Nerita. The semilunar aperture 

 and straight flat columellar lip are its decided 

 characteristics. There are a few species which 

 might pass for Turbines, the columellar lip not 

 preserving its straightness ; but even in these 

 doubtful shells it is flat, and therefore their 

 proper place in this genus is obvious. Some of 

 the species have an umbilicus ; and in some the 

 columellar lip is beset with strong teeth. The 

 Nerites are all either fluviatile or marine, the 

 former are thin and generally have a bright polish 

 on their surface ; nothing can exceed the beauty 

 and delicacy of the minature painting with which 

 many of them are adorned. When viewed 

 through a microscope the most highly finished 

 touches are discernible. They are worn as 

 ornaments by the Indians. They are now 

 formed into a new genus called Neritina. The 

 marine species are distinguished by their solid 

 substantial shells, often having elevated rounded 

 ribs. The animal has a short foot, and two 

 setaceous tentacula, having eyes at their base. 



