PLATE CXIII. 



This species bears much resemblance to Mytilus Cygneus, but 

 differs in being only about half the size, is more compressed and 

 oblong, of a clearer green colour, and the cartilage side extending 

 in a straight line to an acute angle, like a fin, and thence continuing 

 in an oblique line towards the bottom, where it is rounded. — Ex- 

 tremely common in rivers and stagnant waters. 



Pennant's shell is much broader in proportion than our specimens. 



