12 PALUDINIDiE. 



The present shell is so closely allied to the last, that we 

 shall merely particularise the essential differences. The 

 shape is more produced ; the colouring paler ; the sub- 

 stance generally more solid and less translucent ; the 

 whorls less swollen and regularly shelving from their 

 suture in an arcuated line ; the aperture more contracted 

 posteriorly ; the umbilicus more or less concealed. The 

 young shells are furnished with numerous close ciliated 

 spiral lines (Gray). 



The animal closely resembles that of the last species, 

 but its mottling is of a coppery rather than golden hue. 

 The tentacles, muzzle and neck lobes (which are slightly 

 unequal and plain-edged) are palest ; the eye-bulgings very 

 dark. The central and first lateral denticles of the tongue 

 have their apical lobes more developed than in Listeri. 



It inhabits the Thames district in similar situations 

 with the last, and has a similar continental range. 



BITHINIA, Gray. 



Shell turbinated with a produced spire, whorls more or 

 less rounded, covered with a horny epidermis ; mouth 

 ovate, slightly angular above ; peristome thickened within, 

 continuous. 



Animal with a lengthened muzzle ; head bearing two 

 setaceous tentacula with eyes at the external bases. Ten- 

 tacles of male equal. Male organ exserted, reflected into 

 branchial cavity. Mantle lax. A small veil on one side 

 of the neck. Foot oblongo-triangular, obtuse, and not 

 grooved behind, bearing an operculum which is shelly on 

 the inner surface, and has a subcentral nucleus. Branchial 

 plume single. Tongue very short ; similarly constituted 

 with that of Paludina. 



