199 



mit does not turn in an oblique spiral curve, as in the 

 genera mentioned, but is straight, turned quite to the 

 base, and concave beneath ; the left margin flattened, 

 sharp, and straight, forming a flat internal deck or par- 

 tition, which covers a part, but never half the cavity 

 of the aperture; a solid flat operculum, with one late- 

 ral and subulate tooth (or appendage). 



Navicella elliptica Navicella lineata 



Navicella tessellata. 



ifi 



NERITINA. 



NERITA PULLIGERA. Gmclin. 



Chem. 9, M 14,/ 975, 976. 



Naturalists have hitherto confounded the shells of 

 this genus with the true Neritae, which in form they 

 greatly resemble ; but from the circumstance of the 

 latter inhabiting the sea, and the Neritinae fresh water, 

 Lamarck was induced to conjecture the animals were 

 differently organized, and that the shell would conse- 

 quently furnish some proof to that effect, which on ex- 

 amination he found to be the case. The Neritinae are 

 in general of a thin substance; the most part smooth 

 on the surface, or merely finely striated: in all the spe- 

 cies known the right side of the aperture does not pos- 



