2l6 LAKES AND RIVERS, 



brown or almost black, with sometimes a faint tint of 

 blue covered with black or dark gray spots. The length 

 is o'5, the breadth is 0-2. It has 6 or 7 whorls. The 

 shell is oblong, spindle-shaped, yellowish or reddish- 

 brown, faintly striate by the lines of growth ; has a dull 

 greenish-coloured body, with small black and white 

 spots. The foot is bordered with yellow ; the tentacles 

 are broad and flat, and the eyes small. The shell 

 is semi - transparent horn colour, 4 or 5 swollen 

 whorls, a small sharp-pointed spire. The length is 

 1*125 j tne breadth, 0-825. The other species 



LIMN^EA STAGNALIS. 



of the genus Physa, P. fontanalis, has an oval, 

 thin, glossy, transparent shell, 4 or 5 swollen whorls, 

 the last occupying more than three-fourths of the 

 shell. The body is lustrous, dark gray, with some- 

 times a tint of yellow or violet. The varieties 

 are inflata, half as large again as the usual size, the 

 whorls angular towards the suture, the middle one 

 more prominent ; curta, with a very short spire ; 

 oblonga, with a long spire ; and albina, with a milk- 

 white shell. It is found on water-cresses and other 

 aquatic plants in brooks, and also in still waters. 



