89 



Fam. 3. PALUDINIME. 



The tentacles elongate, slender, with eyes sessile at 

 the outer side of their base (p. 78. f. 7. and 9.) ; 

 the gills are always enclosed in the gill cavity. 

 Shell conical, thin, covered with an olive perios- 

 traca ; mouth ovate, entire, angular behind ; the 

 peristome continued ; operculum horny or shelly, 

 formed of concentric laminae, with a subcentral 

 nucleus, (p. 78. f. 8. and 11.) They are all 

 fluviatile. 



The animals were confounded by Lamarck, in his 

 first works, with the genus Cyclostoma ; and Drapar- 

 naud has placed in this genus some marine species which 

 belong to Littorina ; Cuvier, overlooking the cha- 

 racter of the operculum, and some other peculiarities 

 in the animal, confounded them with the animals 

 of that genus. (See Reg. Anim. and Mem. Moll.) 



This family, unlike most of the families of Pteno- 

 branchous Mollusca, consists entirely of truly fluvi- 

 atile animals. 



It has many characters in common with the exotic 

 family of apple-snails (Ampullariadce)^ which also 

 have an annular operculum ; but these have pedicelled 

 eyes, very long tentacles, very long subulate lips, and 

 are furnished with an air-bag on the side of their gills. 



It contains two British genera, which, though very 

 distinct and easily characterised, have been generally 

 confounded, viz. : 



