122 CONCHOLOGY. 



iV. corona. The crown Neritina. PI. 21, fig. 4. 

 Species provided with long spines, and with the columellar 

 edge denticulated. 



N. auriculata. The eared Neritina. 



Species with the columellar edge denticulated ; the two 

 extremities of the right edge extending beyond the aperture, 

 and forming with the callosity, which is reflected over the 

 columella, a kind or ear, produced by the tentacular lobe of 

 the animal. 



N. ■pe7'versa. The perverse Neritina. 



Species shaped like a Calyptraea, with the superior sum- 

 mit vertical, spiral ; the last whorl forming all the base of 

 the shell. 



2. Navicella. Three species, 



A fresh-water shell, closely allied to the Neritina ; it gen- 

 erally has the appearance of porcelain. 



Shell ovate oblong, covered with epidermis, shaped like a 

 Patella, summit not spiral, but straight, turned quite to the 

 base, and concave beneath ; no columella ; the columellar 

 edge replaced by a kind of sharp partition, which covers part 

 of the aperture, with a sinus at its left extremity ; muscular 

 impression shaped like a horseshoe, open in front and inter- 

 rupted behind ; thin, calcareous operculum, with a subulate, 

 lateral tooth adhering to the posterior margin; the other 

 edges sharp. 



Navicella elliptica. Navicella lineata. 



N. tessellata. . 



A", elliptica. The oval Navicella. 



Shell covered with olive epidermis, under which it is 

 smooth, shining, spotted and streaked with purple, blue, or 

 brown ; spire curved, prominent, extending beyond the 

 margin. 



