lineated over their whole surface : lateral teeth entire ^ 

 posterior cicatrices rough, the smaller one orbicular : ante- 

 rior edge blackish. 



OBSERVATIONS. 



The species to which this makes the nearest approach, 

 is undoubtedly the undulatus, Barnes ; but it is more 

 transverse, more oblique anteriorly; the edges of the 

 hinge margin and of the anterior slope are not undu- 

 lated, the umbonial slope is elevated into a distinct sep- 

 arating rib ; and it is of a fine livid purple colour within. 

 The eroded surface of the umbones is perlaceous, irides- 

 cent, and at the apices it exhibits a dull waxen yellow sur- 

 face. 



For this interesting species I am indebted to Mr. Joseph 

 Barabino of New Orleans, who informs me that it inhabits 

 Bayou Teche in the parish of St. Mary, Louisiana. 



REFERENCE TO THE PLATE. 



The plate represents exterior, interior and back views, 

 PI. 33. 



UNIO GLEBULUS. 



SPECIFIC CHARACTER. 



Oval orbicular -, lateral teeth remote, very short, granu- 

 lated. 



PI. 33. 



