165 



ally ou the hinge laminae. In its youth it somewhat resembles 

 the sulcatus, Lea, but is distinguished by many characters, and re- 

 markably by being destitute of any sulcation anteriorly. The 

 largest one I have seen was nearly four inches in its greatest 

 diameter ; but this is gigantic for the species. PL 14. 



Unio subtentus. — Specific cJiaracter. Transverse ; anterior 

 dorsal margin sculptured with small elevated costse. 



Unw subtentus, nobis. Jour. Acad. Nat, Sc. vol. 5, ^j. 130. 



Obs. In general outline this shell has some resemblance to U. 

 purpurcm,* nob. ; but is distinguished by many characters, and 

 more obviously by the character of the anterior costated margin. 

 PI. 15. 



Unio undulatus, Barnes.f — Specific character. Transversely 

 undulated ; umbo literate. 



Unio undulatus, Barnes. Silliman's Journal, vol. 6, p. 120, pi. 2. 



Desc. Transversely oval, somewhat oblong, with large, distinct 

 undulations, three or four in number, directed towards the anterior 

 margin and not proceeding directly from the umbo : surface with a 

 few abbreviated, longitudinal lines, placed without any regularity : 

 umbo placed far backward, not prominent, hardly elevated above 

 the general curvature, more or less literate with short, irregular 

 lines, or slight elevations : hinge margin compressed, nearly recti- 

 linear, prominently angulated or subalated at tip, in the more per- 

 fect specimens with numerous, connected, regular lines, curved to 

 the edge and undulating it : anterior margin rectilinear from the 

 extremity of the hinge margin to the rounded inferior half, and 

 undulated by the tip of the grooves of the disk : posterior margin 

 very short, regularly rounded : base very obtusely rounded, in many 

 specimens a little contracted near the anterior termination : fosset 

 elongated, very distinct : within bluish-white ; perlaceous. 



This large and handsomely sculptured shell, was found in the 

 Fox river of the Wabash, by Mr. Lesueur and Dr. Troost. 



It resembles U. plicatus, nob., but on comparison it will be ob- 



* Although. Mr. Lamarck quotes the proper name of this species as a 

 synonym, yet he has by some error changed it it to purperascens. That 

 it is an error is to be inferred from the observation under his description 

 of U. carinifera, where he says, " trSs-distinct de I'U. purpurea,'''' 



t [This is U. heros of N. H. Dis. ii, p. 291.— Ed.] 



