GASTEROPODA. 



185 



rocks. Many of them, as the Achatina zebra, are covered 

 with a thick epidermis, but others are destitute: a few 

 are constantly reversed or sinistral shells. The Achatina 

 columnaris is one of the most remarkable of land shells ; 

 it is reversed, and the columella forms a winding pillar, 

 visible within, quite to the summit of the spire.* A small 

 species found in the South Sea Islands is strung by the 

 natives, and used for an ornament. 



Beck has ten, and Albers nine genera, formed out of 

 Lamarck's genus Achatina. 



Halia. Risso. (Priamus Beck.) — Shell 

 egg-shaped, not umbilicated, globular, thin, 

 with short spire ; the aperture triangularly 

 oval, beneath with a deep notch ; columella 

 rolled in ; outer lip sharp. — 1 species ; also 

 fossil. 



Brought from Portugal; but, according 

 to Beck, the animal forms an operculum, 

 and is therefore marine. 



Pupa. Lam. — Shell cylindrical ; spire long; aperture 

 irregular, toothed, with the lips thickened, and 

 unconnected at the upper part, the plaits on 

 the left lip intervening. Animal, short, stout, 

 acute behind, its upper tentacles developed, 

 its lower ones short, or almost obsolete.f — 

 150 species; also fossil. 



They are found principally in Europe, but 

 a few species are from America; they derive 

 their name from the resemblance of the shell 

 in shape to the pupa or chrysalis of an insect, and one 

 is named the Pupa chrysalis. — Several species are found 

 in England under stones, old walls, and in woods. 



* Sowerby. 



f Forbes's British Moll. 



