41 



UNIO MYTILOIDES. 



Plate XX. 



DESCRIPTION. 



Shell elevated, subtriangular; epidermis reddish- 

 brown, with crowded wrinkles; posterior side with a 

 broad furrow; anterior side gibbous; umbo tapering, 

 curved, narrowed at the summit, which is much ele- 

 vated; lunule obtusely cordate; within white, purple, 

 and iridescent towards the posterior extremity; car- 

 dinal teeth large, very thick, prominent, sulcated; 

 posterior muscular impressions impressed, the smaller 

 one profoundly. 



SYNONYMES. 



U. mytiloides, Raf. Ann. gen. des Sc Phys. vol. v. p. 47. pi. 82. 



fig. 8. Poulson's trans, p. 53. 

 U. rubra, Raf. 

 U. pyramidatits, Lea. Trans. Amer. Philos. Soc, new series, 



vol. iv. p. 109, pi. xvi. fig. 39. 

 U. caridiacea, Say of Guerin. 

 Cab. A. N. S. No. 2017. 



OBSERVATIONS. 



This common species, since its first discovery in 

 the western waters, has always been known by the 

 name we have adopted. It is nearly allied to U. cor, 

 Nob., and U. undatus, Barnes, but is very distinct, 

 although its varieties are intricate and perplexing. 

 Young specimens are very short and greatly elevated, 

 and frequently rayed; old shells are compressed, cu- 



