OF MOLLUSCA. 113 



There is an appendage on each side of the head, arising from the 

 back of the tentacles ; that on the left side is small, on the right 

 larger before ; the hind portion forms a canal as in Ampullaria. 

 The muscle of attachment is double, the left portion the smallest. 

 Tentacles conical, with the eyes nearly at the base. 



The American and European species are viviparous ; the young 

 are covered with spiral bands of hairs, varying in number in the 

 kinds. There are only five lines in V. fasciatus, and many close 

 lines in V. achatina. 



The Vivipari are sluggish, feeding upon living and decayed 

 vegetable matter, preferring nearly stagnant waters or very sluggish 

 rivers with a bottom of soft mud ; the extension of the foot in front 

 prevents them from taking food except when at rest. They are 

 rarely found reversed ; a reversed specimen of V. decisus was named 

 V. heterostropha by Kirtland. 



The animal of Viviparus decisus of North America is yellow or 

 bluish, with numerous orange spots on the head, tentacles and foot. 

 Tentacles black-tipped ; under side of the foot with light lines 

 radiating from the centre to the edge. They live in ponds and 

 muddy streams, usually concealed under the shelving banks or im- 

 bedded an inch or two among loose mud and roots. The apex of 

 the shell is generally eroded ; the young are excluded in a living 

 state with three whorls to the shell. 



Viviparus ponderosus, which Deshayes considers an Ampullaria, 

 and Say a Melania, has the true horny operculum and the viviparous 

 habit of Viviparus. 



Lamarck, in his first work, confounded the Vivipari with the 

 genus Cyclostoma, and Draparnaud has placed in his genus some 

 marine species belonging to Littorina. Cuvier, overlooking the 



Fig. 59. — Viviparus vulgaris. Eggs with young and gills seen through the shell. 



character of the operculum and some other peculiarities in the 

 animal, confounds them with the animal of Littorina. 



Ferussac, overlooking the structure of the operculum of Vivipari 

 and the number of series of gills, observes, " "We are obliged to re- 

 unite the genera Paludina and Melania of Lamarck ; their animals 

 are perfectly similar, and their shells often so analogous, that one is 

 embarrassed to know which genus to refer them tol We put with 

 them also the genus Rissoa, which is operculated, but we do not 

 know its animal." — Tabl. Syst. Moll. ii. xi. 



