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CHAPTER XXXI II. 



OF THE NERITA. GENUS XXX, 



NERITA. 



"Animal a Linutx. Shell univalve, spiral, gibbous, under side flattisli : 

 aperture half round, pillar lip transverse, truncate, flattish." — Linn. 



1 HIS genus is very distinct from every other. Linnseus makes 

 three divisions in it : the first, wliich is named Vmhilicatce, 

 is also very different from the other two ; the second is imper- 

 forate without teeth ; and the third imperforate with teeth. 



The essential character consists in the aperture or mouth 

 being half round (but not lunate or horned), the pillar lip 

 being straight ; many of the species are strong, thick, opake 

 shells, especially the third division. The pillar lip in the im- 

 perforate shells of both second and third divisions is so diffe- 

 rently constructed from that of any other genus, that these 

 shells may be distinguished at first sight. In the vmibilicated 

 shells the form of the mouth approaches more to that of some 

 species oi Helix, but in most cases is sufficiently distinct fi'oni 

 them. 



There is a considerable difference in the general form of 

 the shells of the first and third divisions, the first being nearly 

 globularj like some Helices, and the third somewhat approach- 



s2 



