PALUDINA. 55 



described by European authors as distinct species; but 

 they appear only to differ from the typical kind in size 

 and colour, as well as in the spire being more or less 

 excentric. In adult specimens, the septa or internal 

 walls of the spire are wanting, and appear to have been 

 absorbed, as stated by Dr. Gray. This is also the case 

 in Melampus or Conovulus, 



Family 11. PALUDINID^. 



Body elongated, spiral, and having a prominent snout : eyes 

 placed outside the tentacles at their base : gill inside the 

 mantle : sexes separate. 



Shell having a long symmetrical sjm^e and an oval mouth : 

 operculum also oval, irregularly concentric or paucispiral. 



These mollusks are, as well as those of the last family, 

 herbivorous ; but they differ in being ovoviviparous, in- 

 stead of oviparous. Their habits are much more active 

 than those of the Neritida. They sometimes, but rarely, 

 float. The fry are furnished with opercula before they 

 are excluded by the mother. According to Bouchard- 

 Chantereaux, the young remain in the ovary, to the num- 

 ber of 20 or 30, for two months, at the end of which time 

 only 2, 3, or 4 are born, the period of accouchement ex- 

 tending over several days. 



Genus I. PALUDI'NA*, Lamarck. PI. III. f. 5, 6. 



Eyes placed on short pedicles or footstalks : operculum horny, 

 irregularly concentric, and having its nucleus on the inner 

 side. 



Lister and Cuvier have investigated, although at very 

 distant intervals, the anatomy of these mollusks, which 



* Inhabiting marshes. 



