The tuberculated beaks are somewhat like those of the 

 figure 9, plate 248 of the Encyclopedie Methodique, 

 but that is represented to have the lamelliform teeth. — 

 The largest individual I have seen measures three inches 

 and a half long, by five and six tenths broad and two and 

 a half inches in convexity. In a particular, oblique, re- 

 flected light, the surface exhibits a tinge of dark green. 



I have recently received several specimens from Mr. 

 Barabino of New-Orleans, near which city he obtained 

 them, and where they are probably not uncommon. He 

 did not state the precise locality, but I presume they inhab- 

 it the sluggish waters in the rear of the city, and not in the 

 Mississippi. 



REFERENCE TO THE PLATE. 



Three views are exhibited of the shell. 

 PLATE XXI. 



