19 

 UNIO RETUSUS. 



Plate VIII. 

 DESCRIPTION. 



Shell transversely ovate, ventricose, with concen- 

 tric furrows; umbo very prominent, curved forwards; 

 beaks retuse, medial; ligament long and prominent; 

 umbonial slope rounded, undefined; anterior and basal 

 margins regularly rounded; posterior side with a 

 slight furrow, and emarginate at the extremity; liga- 

 ment slope arcuate, very oblique; within dark purple, 

 margined with white. 



SYNONYMES. 



U. retusa, Lam. An. sans vert. vol. vi. p. 72. Ferus. Mag. 



de Zool. 

 U. torsa, Raf. Ann. gen. ties Sc. Phys. vol. v. p. 45. pi. 



lxxxii. fig. 1, 2, 3. Poulson's trans, p. 40. 



OBSERVATIONS. 



This fine species is remarkable for the elegance of 

 its form, and the prominent curved beaks which 

 somewhat resemble those of an Isocardia. The colour 

 of the nacre is remarkably constant. One variety is 

 deeply sulcated and emarginate posteriorly; another 

 is entire. Young shells much resemble U. subrotun- 

 das, Raf. Common in the western waters. I did 

 not observe it in Alabama. 



