137 



CHAPTER XXIII. 



NEMTINA OF THE STREAMS. PALUDINA AND HER YOUNG. — CHARACTERS 



AND SPECIES. — BITHINIA. HABITS. — VALVATA. 



WEBITIDJE AND PAIiUDINID^. 



'^ERiTm A fuviatilis. — Adhering to stones by the sides of 

 running streams of fresh water, may be seen the little mol- 

 lusc whose specific name tells the story of its life. The 

 rivers which flow out into the sea on the eastern and western 

 sides of England are its favourite haunts ; it is found in the 

 Thames, the Trent, the Severn, and the Avon. The shell is 

 oval, with a very small flat spire, and a large half-moon- 

 shaped aperture; the outer surface is susceptible of great 

 variation in painting, of which a kind of network of pur- 

 plish-red is the most common. The animal is rather white, 

 with the head and proboscis black, and a black line running 

 along each tentacle -, the eyes, fixed upon pedestals, are also 



