84 PHYTOPHAGA. 



look like pieces of dirt, and thus escape being seized 

 on by the fish. 



The continental conchologists have described several 

 species allied to the above. Rossmasler reduces them 

 to three ; but, from the specimens which I have re- 

 ceived under different names, I greatly doubt if they 

 are more than mere local varieties of our species. 

 Nilson found a small variety or species in Sweden, 

 on the shores of the Baltic, with Mytilus edulis, Cardi- 

 um, &c. Our species has been founcl in similar situ- 

 ations in Loch Stennis, Orkney, by Mr. Edward 

 Forbes. 



