nate; posterior margin rather prominent, but very short; 

 base often a little contracted in the middle ; within pale 

 lilac; cardinal teeth oblique, compressed, denticulated; 

 lamelliform teeth slightly arquated, granulated and striated 

 at tip ; posterior accessory cicatrix rounded, rather deep ; 

 anterior margin somewhat iridescent. 



SYNONYMS. 



Unio ateb, Lea. Trans. Smer. Philos. Soc. Vol. 3, 

 pi. 7, New Series, 



OBSERVATIONS. 



I received several specimens of this shell from Mr. 

 Barabino, who obtained them from Bayou Teche, Parish 

 of St. Mary, Louisiana. It seems to be intermediate, and 

 almost connected by means of varieties, to U. cariosus, 

 Nob., and ventricosus, Barnes ; like those species it has the 

 posterior side prominent and very short, the anterior mar- 

 gin often truncate and the primary teeth often double in 

 both valves ; but however close this alliance may be, it 

 can be distinguished by its somewhat different habit. It 

 is differently coloured, less cylindrical than cariosus and 

 proportionally longer and more cylindrical than ven- 

 tricosus. 



In the young state the ligament margin appears to be 

 coalite, and that of the older shell retains this union on its 

 anterior portion. 



