CHAP. VII. THALLICERA. AMPULLARINJE. 197 



and its habitat, and to the pulmonary fiuviatile Lim- 

 nacince by its animal, there can be no doubt. 



(182.) The shape of the AmpullarincK is most like 

 the garden snails ; they are generally globose, the spire 

 very short, and the body-whorl enormous. Many of 

 them are very large, and none are of a small size. They 

 abound in the rivers of tropical countries, both of the 

 New and the Old World. Guilding has admirably de- 

 lineated the animal of this and the sub-genus Ceratodes, 

 and has thus determined the latter to be a representa- 

 tive only of Planorbis. The animals, in fact (fig. 35.), 



of the present group are furnished with a respiratory 

 siphon (a) ; and are, no doubt, carnivorous, as well as 

 herbaceous. Most of them have the operculum horny, 

 but in some it is shelly j and this, joined to the thin- 

 ness or thickness of the outer lip, may serve to dis- 

 tinguish the sub-genera. The genus Paludina seems 

 to represent the last in the rivers of Europe, and is 

 well distinguished by the greater length of the spire, as 

 seen in our native P. vivipara; but there are many 

 exotic species : the aperture is narrowed above, and 

 generally protected by a horny operculum. Nematura 

 appears a sub-genus whose operculum is shelly, and 

 the aperture still more contracted. With this genus 

 o 3 



