MOLLUSC A OR UNIVALVES. 189 



57. Ampullaria. — Shell generally large, 

 thin and globular ; spire 

 very short; mouth semi- 

 circular, with the lips united, 

 the outer being acute ; oper- 

 culum thin and horny, and 

 rarely calcareous ; the shell 

 has an epidermis, and an umbilicus varying in 

 size. Animal having a large head furnished 

 with four tentacula, with eyes at the base of 

 the two longest ; foot oval and large. — 27 

 species recent, and 16 fossil. 



The Mollusca forming this genus are found 

 in the rivers of Africa, India, and South Ame- 

 rica, but have not been discovered in Europe 

 or North America. They are found in rivers 

 and ditches ; one species, the Ampullaria 

 ovata, inhabits the Lake Mareotis, where the 

 water is salt, and another the brackish 

 water near Rio de Janeiro. # Some of the 

 African species have reversed shells, and all 

 that are natives of Africa and America have 

 the operculum horny : those, on the contrary, 

 which come from India, have it usually shelly, 

 * Darwin. 



