174 



MANUAL OF THE MOLLUSCA. 



Animal with short, tapering and rather compressed tentacles ; foot di- 

 vided transversely into two portions, advanced successively in walking. 



Listr. W. Indies, Europe. In salt-marslies and on the sea-shore. The 

 British species have thin ovate shells, Avith the spii-e moderately produced, 

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

 Leach. Fossil. Eocene. Brit. France. 



Cakychium, Miiller. 



Type, C. minimum, PI. XII. fig. 39. 



Syn. Am*icella, Hartm. 



Shell minute, oblong, finely striated transversely ; aperture oval, toothed, 

 margins thickened, united by callus. 



Animal with 2 blunt, cylindiical tentacles ; eyes black, sessile, near to- 

 gether, behind the tentacles. 



Distr. 3 sp. Europe; N. America. At the roots of gi'ass in damp 

 places, especially near the sea. 



Fossil. Miocene — . Europe. 



The genus SipJionaria, described at p. 155, is supposed to be pulraoni- 

 ferous, 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. 



e^>!^^^^ 





Fig. 100.* 



SECTION B. Opekculata.* 

 The Operculated land-snails are exceedingly like periwinkles {litorincB), 

 and chiefly differ from them in the situations they inhabit, and the medium 

 respired. They have a long truncated muzzle, 2 slender contractile tentacles, 

 and the eyes are sessile on the sides of the head.j The mantle-margin is 

 simple, and the pulmonary cavity is situated on the back of the neck, and 

 quite open in front. Lingual ribbon narrow ; teeth 7-ranked. 



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

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



+ Phanero-pneumona (open-lunged), Gray. The account of this group is chiefly 

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



J The tentacles of the helicidcs are retractile, by inversion (p. 25) those of the 

 cyclosiomidce are contractile only. 



