26 PALUDINID^E. 



B. TENTACULATA. 



Umbilicus practically 



none. 



Mouth obliquely oval 

 and sharply angulated. 



B. LEACHII. 

 Whorls much more con- 

 vex. 



Suture much deeper. 

 Umbilicus distinct. 





 Mouth almost circular. 



Genus III. HYDROBIA. 



1. H. SIMILIS (similar to another species). 

 Sub-conical, thin, semi-transparent, yellowish horn- 

 colour ; whorls five to six, rounded ; suture deep ; mouth and 

 operculum oval ; umbilicus small. 



This species is only found between Greenwich and 

 Woolwich, in ditches which are occasionally flooded 

 by the tide. 



2. H. VENTEOSA (swollen). 



Conical, tapering, thin, glossy, semi-transparent ; whorls 

 six to seven, rounded ; spire pointed ; mouth oval. 



Abundant in brackish water in estuaries in England 

 and Wales. 



Var. I. minor. Much smaller, spire shorter. 

 Var. II. decollate Truncate, eroded. 



