135 



land, widely spread (Forbes), Livingstone, Wes 

 Lothian (Flerainff), Isle of Man, rare (Forbes). 



On the continent, in France (Draparnaud), in Ger- 

 many (Pfeiffer), and in Sweden (Nilson). 



This species can live even longer out of its native 

 element than Planorbis vortex. 



Planorbis contortus [The Twisted Coil Shell]. 

 Linnceus. 



Figures 99 and 100. 



First described by Petiver. 



A dull lookinjj horn-coloured shell, having the upper 

 disc flat, and the lower disc deeply sunk in the middle, 

 so as to form a profound umbilicus. There are from 

 five to six very narrow convolutions, the body whorl 

 being scarcely larger than the preceding one. Aperture 

 lunate, and very smaJl. The shell is very deep for its 

 diameter, the difference in length and width being 

 rather more tbfin as two to one. Suture deep. 



Average diameter a fifth of an inch, and average 

 height one line. The largest specimens, sent fiom 

 Stone by the Rev. J. B. Reade, and those found by ray" 

 self at Lytham, measured fully two lines and a half by 

 more than one line high. 



The colour of the animal is somewhat leaden. 



Asomewhat common shell, inhabiting ditches, ponds, 

 and slow streams. 



M. Bouchard Chautereaux says it lays from six to 

 eight eggs at one time, which are hatched in from ten 

 So twelve days. 



