GASTEROPODA. 



07 



at the outer base ; the tongue is slender, long, and linear, 

 having in the middle a row of teeth, and on each side three 

 rows of hooks, and lying partly in the intestinal cavity. 

 The shell is spiral, of various forms, with a notch or canal, 

 or entire at the base. Either marine or fluviatile. 



Paludina. Lam. (Viviparus Cuvier ; Yivipara Lam.) 

 — Shell turbinated, having the whorls rounded ; 

 aperture roundish, angulated above ; margins of 

 the lips united ; covered with an olive epider- 

 mis ; operculum horny. Animal, with a length- 

 ened muzzle, head bearing two tentacula, the 

 extremities of which are setaceous, but the bases 

 thickened by the union with them of the eye peduncles ; 

 tentacles of the male unequal; mantle ample; a small 

 veil on each side of the neck; foot large, oblong, tri- 

 angular, obtuse, and not grooved behind; bearing on a 

 rounded lobe an operculum, which is corneous and com- 

 posed of concentric elements round a central nucleus; 

 branchial plume single, concealed; tongue very short, 

 armed with a transverse series of denticles, each composed 

 of an ovate, central denticle, flanked on each side by three 

 oblong lateral uncini, all with crenated apices.* — 60 

 species ; also fossil. 



This genus is distributed all over the world, and is 

 usually found in fresh waters, rivers, and ponds; there 

 are, however, some species found in salt marshes, but none 

 in the sea. The British species are two, P. vivipara and 

 Lister i. 



In Sussex there are extensive beds of marble almost 

 wholly formed of fossil Paludina. That called Petworth, 

 or Sussex marble, is principally made up of one species, 

 P. fluviorum ; and Dr. Mantell says, " it is an aggregation 



* Forbes's British Moll. 

 II 



