FAMILY NAIADES. 



213 



Anodonta cygnea. 



Genus I. ANODONTA, Lamarck. 



Animal ; body oval, compressed, dingy greyish yellow, mantle 

 fringed and stained with brown at the edge, gills showing a 

 network of waved tubes, foot large, tongue-shaped, tinged 

 with orange. 

 Shell ; equivalve, very inequilateral, thin, rounded in front, ob- 

 liquely produced and a little auriculated behind ; hinge tooth- 

 less, but furnished posteriorly with a long rudimentary tooth- 

 lite ridge. 

 Anodonta, the largest of European freshwater mollusks, is pro- 

 vided with a largely ventricose shell of light substance, which, as its 

 name implies, is without teeth. A strong external ligament affords 

 hinge sufficient for its thinly calcified valves, without the support 

 of any internal interlocking protuberances, yet a tooth of a rudi- 

 mentary kind appears on the posterior side of the shell, in the form 

 of a blunt marginal ridge. The animal has a largely developed foot 

 of an orange-tinted yellow colour, with which it burrows into and 

 trails along the mud, and the mantle margin is fringed and stained 



