46 HELICID^. 



pair of tentacles. Respiratory foramen or cleft, in tlie 

 collar at the angle of the apertvire of the shell, with the 

 anal orifice immediately adjoining. Organs of genera- 

 tion imiting at a single outlet, and opening on the i-ight 

 side, usually a Httle behind the superior tentacle, but 

 sometimes as far back as the collar. Hermaphrodite, 

 but requiring a double union. Herbivorous or carniv- 

 orous. 



Shell. Always spiral, but variable in form, covering 

 the animal entirely, ■without operculum. 



Geographical Distribution. The Heliciclce are 

 spread throughout the tropical and temperate regions 

 on the continents, and islands. They are most numerous 

 near the equator, and diminish in numbers towards the 

 north, until, in the colder latitudes of the temperate zone, 

 they become rare, and are behoved to be entirely want- 

 ing in the arctic circle. Their distribution in the United 

 States, according to their genera and species, has been 

 exhibited in the tables ^ven in the introduction ; but it 

 may be repeated here, in a more condensed shape. Vit- 

 rina is exclusively a northern genus, and has not yet 

 been noticed south of 4-±° of north latitude. GrlamUna 

 is quite as exclusively a southern genus, and is confined 

 to the alluvial lands on the southern Atlantic coast, and 

 the shores of the Gulf of Mexico. Bulimus is also a 

 southern genus, though having a much wider range than 

 Criandina, yet Bulimus hmya may be an exception, and 

 so far as known, is found only in the more northern local- 



