OF MOLLUSCA. 07 



when contracted. From the tentacles on each side to the base of 

 the edge of the respiratory cavity is a continued broad flat plate, 

 which is largest on the left side, and which appears to be bent up, so 

 as to form a canal to conduct the water to the respiratory cavity. 

 The one on the right side is folded, and gives origin to a fleshy ridge, 

 which extends up the right side close to the side of the colon, and is 

 continued to the top of the respiratory cavity. The penis is conical, 

 elongate, near the tentacle, and enclosed in a bivalve sheath, with the 

 thickened margin to the right side of the collar. They live a very 

 long time out of water. Specimens have been brought alive from 

 Egypt and India, kept dry in sawdust. 



The Ampullaria appear to differ in size according to the soil on 

 which they happen to live. In sandy places they are small and 

 thin ; where the soil is more muddy the specimens are larger. — 

 jyOrbigny. 



The Ampullaria insularum of La Plata is found on the large 

 aquatic plants in the marshes on the side of the river, especially such 

 as have a muddy bottom. They lay their large red eggs in groups, 

 in March. They live many months out of the water. They are 

 eaten by the Rails and other water birds, who often break the 

 operculum, the only vulnerable part, to get at the animal. 



Ampullaria canaliculata is generally found on rushes and aquatic 

 herbs ; it also often glides on the surface of the water, shell down- 

 wards. The animal is generally expanded, but it contracts with the 

 least touch. It walks slowly, its tentacles being in constant move- 

 ment. In October its ovaries are filled with a mass of rose-coloured 

 eggs ; they are laid in November, on branches under water attached 

 to a tree or bush out of the water. These eggs are a beautiful rose 

 colour, with a whitish bloom. At the end of two or three days each 

 group is closed; the eggs are then protected by a chalky pellicle, 

 formed by exposure to the air. At the end of fifteen or twenty 

 days, the young animals, which are of a pure rose colour, appear 

 covering all the plants. If rain does not occur within this time, the 

 eggs do not hatch, but the animals perish in the eggs from the 

 drought. The young and old are eaten by the Wading birds, which 

 often take the older ones to a branch of a tree and let them fall, so 

 as to break the shell, and thus get at the animal ; many shells so 

 broken are to be seen at the roots of the trees. 



5. POMELLA. 



Shell half-ovate, solid, striated, imperforate ; mouth very large ; 

 inner lip concave. Peristome simple, thin. Operculum horny, dex- 

 tral, on right margin {Adams, Gen. Moll. t. 37. f. 4 a, b) ; inner lip 

 concave ; shell striated. 



1. P. neritoides. 



The operculum of Pomella neritoides is thick, horny, as large as 

 the mouth of the shell, with the nucleus on the middle of the inner 

 straight edge. They are found at the mouth of the Rio Uruguay or 

 Ampullaria River. They are most like a giant Neritina. 



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