56 RAMBLES IN SEARCH OF SHELLS. 



submerged leaves of Nuphar lutea. It is generally- 

 encrusted with mud, the removal of which appears 

 to destroy the beautiful coloured markings which 

 are so ornamental when the shell is found dead 

 and empty. 



The so-called freshwater limpets, Ancylus flu- 

 viatilis and lacustris, or ohlongus as it is often called 

 (PL VII., figs. 1, 2), furnish another illustration of 

 the fact that both salt and fresh waters have their 

 respective representative forms. Both species may 

 be found in the Thames and the Lea, adhering to 

 stones and leaves of aquatic plants, especially on the 

 leaves of Nuphar lutea, where they furnish abundant 

 food for fish, which push them off with their snouts 

 and swallow them — in much the same way, no doubt, 

 as the Oyster-catcher {Hcematopus ostralegus) over- 

 turns the marine limpet (Patella) with his bill to get 

 at the animal within. The freshwater limpets are 

 frequently sought after as food by the Dipper, Moor- 

 hen, Water-rail, and different species of Grebe, as evi- 

 denced by the fragments of shells which have been 

 found in the stomachs of these birds. They also swal- 

 low the bubble-shells (Physa) and Valvata piscinalis; 

 but, although the Little Grebe or Dabchick may be 



