168 



UNIONID^. 



Interior usually of a beautiful dark peacli-blossom color, and passes 

 from this through salmon-color to mother-of-pearl, tinged violet. 

 Hinge having a single erect, pyramidal, coarsely striated cardinal 

 tooth in the right valve, with the vestige of a tooth before, and a 

 pit behind it ; on the left valve are two nearly equal teeth of a tri- 



Fig. 472. 



V. compUinntus. 



angular, pyramidal form, the space between them corresponding to 

 the opposite tooth ; lateral teeth compressed, long, very slightly 

 curved. Ordinary length, three and one half inches ; height, two 

 inches ; breadth, one inch. 



This is the most connnon fresh-water mussel we have. It is 

 found in every considerable brook or collection of water emptying 

 into the Atlantic ; and it is said never to be found in any of the 

 streams beyond the Atlantic slope. 



It is perhaps the most variable of all species, as we may judge 

 by noticing the numerous species which, according to Mr. Lea, La- 

 marck made of its varieties. And it is to be feared that Mr. Lea 

 himself has not entirely avoided this error. Certain it is, that 

 shells answering well to his Roanokcnsls,jrjimus, and some others, 

 are not seldom found in Massachusetts, among the indisputable 

 complanatus. 



The shell is always rounded before, somewhat widened and angu- 

 lar behind, and slightly truncated at tip, especially if viewed inside. 

 Nor is it ever much inflated. Its true form is transversely oblong- 

 oval ; but is often nearly oval, and sometimes is much curved. In 

 one specimen before me the height is five eighths the length, and in 

 another it is only two fifths. In this latter the breadth is one fourth 

 the length, while in a third it is nearly one half. The epidermis 

 is usually coarsely wrinkled, without lustre, and of a pitchy black 



