SNAILS AND LIMPETS. 185 



ponds and ditohes in different parts of Britain. It is frequently 

 recommended as an inmate of the aquarium, but those who 

 introduce it among their water-plants should remember that it 

 has a very great liking for their tender roots and rootlets, 

 especially those of the duckweeds. With the exception of this 

 weakness, the snail may be considered as useful and harmless. 

 The body of the animal is plentifully, covered with slime ; hence 

 its specific name of glutinosa. It is of a dark grey colour, tinged 

 with yellow and spotted with orange. The tentacles are short, 

 vfery broad at the base, flat, blunt at the tips, and spotted with 

 white. The shell is about Jin. in length, " globosely-ovate " in 

 shape, and of a glossy yellowish horn-colour. There are three 

 or four globose whorls : the body- whorl is considerably larger 

 than the rest of the shell. The spire is produced very little, 

 and the sutures are rather deep. The aperture is almost oval, 

 and the iimer Up is much expanded. This snail lays from 

 twenty-five to thirty eggs, and incloses them in a rounded 

 and transparent capsule. They ai'e hatched in from sixteen 

 to twenty days. 



The little moUuscs called Ancyli are interesting, useful, and 

 harmless in the aquarium. They are very sluggish in their 

 movements, taking a long time to travel even a short distance. 

 They do not swim, nor have I ever seen them float, though I 

 seldom let a day go by without having noticed them and their 

 habits. Their principal food seems to be confervas and decaying 

 vegetable matter. The stomachs of these " fresh-water limpets," 

 as they are sometimes called, have been compared to the gizzard 

 of a fowl, on account of their muscular bands and the minute 

 particles of sand which they are found to contain. The shell is 

 hooked like a hawk's beak ; hence the generic name. There are 

 two species of this genus in Britain : though pulmobranchiate, 

 they are rarely seen to come to the surface of the water for 

 a fresh supply of atmospheric air. 



Aneylus fluviatilis (Fig. 123) inhabits rivers, streams, and 

 other clear water in every part of Britain. It is generally 

 found adhering to stones at the bottom, but occasionally 

 it is taken upon aquatic plants or out of water altogether, 

 though within reach of the spray of waterfalls and the like. 



