174 



PRESH-WATEE AQTJAEIA. 



is sometimes an incli in diameter; the periphery is round. 

 This snail has a ctirious habit of fixing itself by its side to 

 perpendicular surfaces, such as the glass of the aquarium. 



Planorhis carinatus is also a very useful snail in a tank, 

 and very popular with aquarium-keepers. The periphery of 

 the shell, instead of being round as in the last species, is dis- 

 tinctly keeled near the centre. Like P. cornms, it feeds upon 

 confervas in preference to growing plants. It is not a very 

 active animal. P. carinatus is unfortunately by no means 



Fig. 117. Planorbis marginatus. 



•common, except perhaps in the ponds, ditches, and slow- 

 running streams of the Eastern Counties. It is taken in other 

 parts of England, but not in any numbers ; nevertheless, it 

 can generally be bought of aquarium dealers. This species 

 incloses its eggs (six to twelve in number) in capsules shaped 

 like those of P. corneus, and affixes them to stones, leaves, 

 &o., and in addition to these, while in confinement, to the 

 sides of the aquarium. The fry are hatched, according to 

 the temperature of the water, in about fourteen days. The 

 body of the animal is a reddish dark brown. The tentacles 

 are slender and yellowish, with a pinkish tinge ; they are also 



