3320 



THE MOLLUSKS OR SHELLFISH 



are also different in the two genera. The species of Limncea frequent shallow and 

 still waters, in most parts of the globe, often swimming at the surface of the water 

 in an inverted position. They are prolific and gregarious, and the eggs are inclosed 



COMMON POND SNAii, (Limncea'). 



in transparent gelatinous capsules, and deposited in continuous series, and 

 attached to submerged stones as well as to the stems and leaves of aquatic plants. 

 L. stagnates, which is common in ponds, marshes, and slow rivers, is the largest 

 species, and six other species occur in Britain. The other, figured forms illustrate 



VARIOUS FORMS OF THE GENUS 



i. Limnesa glabra ; 2. L, palustris ; 3. L. sta.gna.lis; 4. L. truncatula ; 5. L. peregra ; 6. L. vulgaris ; 7. L. ovata ; 



8. L. auricular ia. 



the great variation which occurs in the relative length of the spire and aperture. 

 In one of these {L. truncatula) the liver fluke, so destructive to sheep, passes one 

 stage of its existence. 



