89 



Tarn. 3. PALUDlNIDiE. 



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 Littorince; 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 ( Ampullar iadce), 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. : — 



