SLL'GS AND SNAILS. 493 



are of some importance, as they exist in great quantities, and form 

 an article of food to our troufr. I have seen the bottom of the Back- 

 water literally covered with the dead shells, and I have known pints 

 of shells to pass through the pipe used to supply our fish-hatching 

 apparatus. The eggs may be seen in an aquarium on the glass, and 

 the little creatures, when first hatching, are interesting objects. They 

 can float upon the surface of the water as though that surface were a 

 solid body to which they could attach themselves. 



In our Central stream, particularly in the fern glen, there are plenty 

 of the common River Limpet (Ancylus fluviatilis, fig. 1092) adhering 

 to the stones where a rapid current of water passes over them. 



Amongst our water weeds we have many of the Planorbis corneus 

 or Horny Coil Shell, the P. carinatus, P. complanatus, P. vortex 

 (fig. 1093), and P. contortus. These creatures are of considerable im- 

 portance to us, affording food for the trout, and it is very amusing to 

 see the fish with tails out of water in the evening diving amongst the 

 water weeds to pick them out. 



FIG. 1096. 



FIG. 1092. FIG. 1093. FIG. 1094. FIG. 1095. Valvata piscinalis. 



River Limpet. Planorbis vortex. Cyclas cornea. Bithinia ventricosa. 



The Cyclas cornea (fig. 1094),- if it does not exist in my garden, 

 abounds in a turf-pit immediately outside in the grounds of Mr. Sheppey. 

 It has a bivalve shell. 



We have two Bithinias, B. ventricosa (fig. 1095) and B. tentaculata 

 both small creatures living in the water ; and also Valvata piscinalis 

 (fig. 1096), another small water snail. 



I had a fancy to acclimatize the Dreissena polymorp/ia, a very curious 

 creature introduced about fifty years ago into the Commercial Docks, 

 and supposed to have come from the Danube. It exists in the reservoirs 

 of the New River Company at Stoke Newington ; but the specimens 

 I placed in my water did not thrive, and I presume the trout devoured 

 them, as sticklebacks were seen to do so when placed with specimens in 



