pression not indented, curved beyond the anterior muscu- 

 lax impression : anterior accessory muscular impression ve- 

 ry large, separate : cardinal teeth transversely long, slen- 

 der, very oblique : lateral teeth distant from the cardinal 

 teeth, tw^o in each valve, equally prominent in the two 

 valves. 



OBSERVATIONS. 



For an opportunity to examine this species I am indebt- 

 ed to Mr. Lesueur, who obtained it in Bayou St. John, 

 near New-Orleans. It is readily distinguishable from any 

 other species. 



UEFERENCE TO THE PLATE. 



Three views are exhibited of the shell. 

 PLATE XXIII. 



