156 MOLLUSCA. 



type of the genus; whereas thetermAmphibulina,is founded 

 on a mistake, and is apt to mislead. The Helix #uccinea, 

 (the type of the genus), although found in damp places, is 

 not amphibious. It never enters the water voluntarily. In- 

 deed Miiller says, " Sponte in aquam descendere numquam 

 vidi, e contra quoties eum aquae immisi, confestim egredie- 

 batur." The same remark is made by Montagu, and we 

 have often witnessed its truth. 



ORDER II. AQUATIC. 



The aquatic pulmoniferous Gasteropoda have their resi- 

 dence constantly in the water. They possess two tentacula 

 only. These are usually flattened, incapable of being with- 

 drawn, and having the eyes at* the internal base. The food 

 consists of aquatic plants. Respiration can only take place 

 at the surface of the water, to which the animals occasion- 

 ally ascend, to expel from the pulmonary cavity the vitiated 

 air, and replenish it with a fresh supply. The sexes are 

 united. The spawn, which is in the form of a rounded ge- 

 latinous mass, containing many ova, is deposited on aquatic 

 plants under water. Previous to hatching, the foetus must 

 be aerated by means of some branchial arrangement. 



GENUS LIMNEA. Aperture of the shell having the right 

 lip joined to the left at the base, and folding back on the 

 pillar. 



The tentacula are lanceolated and depressed. The mouth 

 is furnished with three jaws ; the lateral ones simple ; the 

 upper one crescent-shaped, and emarginate. The male and 

 female organs, though intimately connected internally, have 

 their external orifices separated to a considerable distance, 

 the former issuing under the right tentaculum, the latter at 



