165 
ally on tlie hinge laminae. In its youth it somewhat resembles 
the sulcatus, Lea, hut 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 ; hut this is gigantic for the species. PL 14. 
Unio subtentus. — Specific character . Transverse ; anterior 
dorsal margin sculptured with small elevated costae. 
Unio subtentus, nobis. Jour. Acad. Nat. Sc. vol. 5, 130. 
Obs. In general outline this shell has some resemblance to U. 
purpureus,^ nob. ; hut is distinguished by many characters, and 
more obviously by the character of the anterior costated margin. 
PI. 15. 
Unio undtjlatus, Barnes.f — Specific character. Transversely 
undulated umbo literate. 
Unio undulatus, Barnes. Silliman’s Journal, vol. 6 , 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 
Pox river of the Wabash, by Mr. Lesueur and Pr. 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, “ tres-distinct d.e VU. purpurea.” 
t [This is U. keros of N. H. Dis. ii. p. 291. — En.] 
