196 



FEESH-WATEE AQTJAEIA. 



brown, and the valves are rather swollen. The umbones 

 are placed towards the anterior end, which slopes away rather 

 suddenly in the direction of the ventral margin. The upper 

 part of the posterior side has a " cut-away " or flattened 



Fig. 129. Anodonta cygnea. 



appearance. There are no teeth attached to the hinge; hence 

 the generic name. The muscular scars are indistinct. This 

 species is commonly- called the " Swan Mussel," I suppose 

 because the swans are fond of feeding upon it. 



Dreissena pol/ymorpha is a curious and beautiful little 

 mussel, first described as a native of this country by Mr. J. 

 de Carle Sowerby in the year 1824. It is supposed to have 

 been introduced here by cUnging to the timber brought from 

 the Volga. It has the power of hving for a long time out of 

 water. It also possesses a hyssus by means of which it is 

 able to attach itseK firmly to shells of the larger Conchifera, 

 wood, stones, &c. The shell is described by the author of 

 the excellent little book, "Lakes and Rivers," as "oblong, 

 rising in a sharp keel in the middle of each valve and flattened 

 below, pointed at the end or beak, and gradually but obliquely 

 widening towards the front, solid but not glossy. Beneath 

 the epidermis it is purplish-brown . The beaks (umbones) are 

 terminal." This bivalve is now found in slow-running water 

 in many parts of England. It is said that it has even been 

 discovered clinging to the inside of some of the London iron 

 water-pipes. 



