52 NERITHLE. 



Only three families of this Order inhabit the fresh 

 waters of this country. They are, 



I. NERITID^E. 

 II. PALUDINID^E. 

 III. VALVATID^E. 



All these freshwater Snails have two tentacles, and the 

 same number of eyes, which are placed at the base of the 

 tentacles. Their shells are furnished with an epidermis 

 and operculum. 



Family I. NERITID^E. 



BODY oval, having a short spiral turn at the end : eyes 

 placed outside the tentacles at their base : gill inside the 

 mantle : sexes separate. 



SHELL semiglobose, with an excen trie spire and a semicircu- 

 lar mouth : operculum having an excentric and short spire, 

 and furnished underneath with an apophy sis or projecting pro- 

 cess which locks into the columellar or pillar lip. 



Although the members of this family are very 

 numerous and widely dispersed beyond the limits of our 

 seas, we have only a solitary representative, forming the 

 single species of one genus. 



NERITI'NA*, Lamarck. PL III. f. 1, 2, 3, 4. 



BODY furnished with a strong and prominent snout 

 muzzle : tentacles long: eyes placed on footstalks -.foot broad. 



SHELL triangular-oblong : operculum calcareous and solic 



The mollusks of this genus inhabit waters which hai 

 a stony or gravelly bottom. Their habits are sluggish 

 raising their shell but little during their march, and tht 

 only showing their tentacles, eyes, and the front of theii 



* Diminutive of Nerita, a genus of marine shells. 



