GASTEROPODA. 305' 



Shell obtusely cone- shaped, smooth ; spire short, flat-whorled ; 

 aperture long, narrow ; lip sharp, denticulated within ; colu- 

 mella twisted in front ; wall of the aperture with 1 or 2 spiral 

 plaits. 



Animal vdih. short, tapering, and rather compressed tentacles ; 

 foot divided transversely into two portions, advanced successively 

 in walking. 



Distribution, 56 species. "West Indies, Europe. In salt' 

 marshes and on the sea-shore. The British species have thic 

 ovate shells, with the spire moderately produced, and the aper- 

 ture oval. They form the sub-genus Alexia (denticulata), 

 Leach. 



Fossil, Eocene. Britain, France. 



Caeychitjm, Miiller. 



Type, 0. minimum, PI. XII., Eig. 39. 



Synonym, Auricella, Hartm. 



Shell minute, oblong, finely striated transversely; aperture 

 oval, toothed, margin thickened, united by callus. 



Animal, with 2 blunt, cylindrical tentacles ; eyes black, 

 sessile, near together, behind the tentacles. 



Distribution, 9 species. Europe ; North America. At the 

 roots of grass in damp places, especially near the sea. 



Fossil, 3 species. Miocene — . Europe. 



The genus Siphonaria, described at p. 281, is supposed to be 

 pulmoniferous, and to bear somewhat the same relation to 

 Auricula that Ancylus does to Limnaea. The lingual dentition 

 is similar to Auricula ; the centre teeth are distinct, the laterals 

 numerous and hooked. 



Fig. 133.* 



Section B. — OPEECTJLATA.f 

 The Operculated land-snails are exceedingly like periwinkles 



* Siphonaria species from the Cape ; three rows of teeth, c central, I laterals, from a 

 preparation by J. W. Wilton. Esq., of Gloucester, 



t Phanera-pneumona (open-limged). Gray. The account of this group is chiefly 

 taken from the catalogue prepared by my friend Dr. Baird. 



