51 



posterior basal margin emarginate; epidermis smooth, 

 shining, yellowish with numerous green rays; within 

 white, rarely rose coloured. 



SYNONYMES. 



U. gibbosus, Raf. Ann. gen. des Sc. Phys. vol. v. p. 49. Poul- 



son's trans, p. 56. 

 U. torulosus, Raf. lb. p. 48. Poulson's trans, p. 56. 

 U. perplexus, Lea. Trans. Amer. Philos. Soc. new series, vol. 



iv. p. 122, pi. 17, fig. 42. 

 Cab. A. N. S. No. 1051. 



OBSERVATIONS. 



Besides its affinity with the preceding species, this 

 shell has a general resemblance to three others, with 

 none of which, however, can it be confounded by 

 those who are familiar with the subject; these are 

 U.flexuosiis, U. Phillipsii, and U. rejiexus. 



Common in the Wabash and Scioto, and I have 

 found it in the Tennessee river, at Florence, Alabama, 

 but not farther south. The female may be readily 

 distinguished by the dilated margin, which is more 

 profound in this species than in any other. 



UNIO GIBBOSUS. 



VARIETY PEROBLiaUUS. 

 Plate XXVII.— Fig. 2. 



OBSERVATIONS. 



This is perhaps a mere variety of U. gibbosus, Raf., 

 but it is much more oblique, the beaks nearer the 



