GASTEROPODA. 



197 



Stoastoma. Adams. — Shell globose, with a semi- 

 circular aperture; the outer lip not reflected, but pro- 

 duced beyond the inner lip, from which it is 

 separated by a little groove ; operculum 

 calcareous, outwardly deeply concave, with 

 laminated, slightly elevated, irregular m- Stoastoma. 

 creasing striae. Animal not known. — 12 

 species.* 



Very small shells, of a globose form, found in Jamaica. 



Helicina. Lam. (Oligyra Say ; Pitonnillus Montf.) 

 Shell flattened; mouth semicircular, closed by a horny 



operculum ; lip thickened, and columella often also thick- 

 ened. Animal, having a head furnished with a proboscis, 

 and two tentacula, with eyes at the base on tubercles; 

 foot rather short. — There are 90 species ; also fossil. 



Some species live on trees, and others on the ground ; 

 they are natives of the West Indies and other countries of 

 the torrid zone. The operculum, which is permanently 

 attached to the foot, is not spirally formed, but in con- 

 centric layers. — The H. viridis from St. Domingo, is of a 

 smooth shining green colour. 



Philippi places the following as sub-genera : — Trocha- 

 tella and Lucidella Swain. 



* Sowerby's Conchological Manual. 

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