1H UNIVALVES. 



underneath ; aperture semi-lunar entire ; colu- 

 mellar 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 charac- 

 teristics. There are a few species which might 

 pass for Turbines, the columellar lip not preser- 

 ving 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 sur- 

 face ; nothing can exceed the beauty and delicacy 

 of the miniature painting with which many of 

 them are adorned. "When viewed through a mi- 

 croscope the most highly-finished touches are 

 discernible. They are worn as ornaments by the 

 Indians. These are now formed into a new genus 

 called Neritina. The marine species are distin- 

 guished 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. 



