abruptly terminated before, but gradually diminishing 



of some Alasmodontas:; lateral teeth rather slender. 



Length (at the anterior tip of the lateral teeth) one inch and 

 one-fifth; breadth, nearly two inches and one-fifth. Con- 

 vexity, four-filths of an inch, inhabits Mexico. 



This shell is remarkable for the coppery tint, which is more 

 obvious on the umbones. It was obtained in Lake Ch 

 and was presented tome by Mr. Maclure. Jn the young state 

 it is radiate with green before, and the adult has a % 

 granular deposite of carbonate of lime, on the anterior half of 

 the shell, Which is in the water and above the mud. 

 species appears to be abundant. 



U. subrostratus. Transversely elongated, subrostrated, ra- 

 diated. 



Inhabits Wabash. 



Transversely elongate subovate, brownish or pale ochreous, 

 with numerous dark green radii: beaks but little elevated with 

 a few, small angular, concentric lines: ligament margin a little 

 compressed: anterior margin somewhat elongated, hardly sub- 

 rostrated: separated by an obtuse angle from the ligament 

 margin: base arquatcd: posterior margin rounded: within w 

 often slig .tly tinted with flesh color; somewhat iridesccn 

 the margins, particularly the anterior margin: substance of 

 the shell not thick: teeth very oblique, crested. 



Length, one inch and two-fifths; breadth, three inches 

 one-fifth. Convexity, hardly over one inch. 



This may be said to be the anologue of the U. nasuhts, T- 

 of the vVestern waters. The rostrum however is not so defi- 

 nite, and it is a more convex shell. The aged shell is dark 

 brown, but near the beaks reddish brown. 



Note. — A short time since, I began a review of the American species of Unio 

 hithen bj naturalists, in which it appeared to me that much yetn i 



to be done, notwithstanding the laudable attempts that have air. ady be< n m 

 rectify tii» s\ noiiwiia: but on advancing somewhat in the undertaking, 1 found my- 

 self so much at a loss for hooka and oth< r ru< ao9 of 1 1 



ence, that I was compelled for the present to relinquish it. The following I 

 however, 1 have concluded to publish, because it r< iates to the i imon Bpe 



cies in our eastern waters. 



U. purpureus, Nob. The propriety of retaining th 

 has recently been much questioned by two of our concl 

 ists, but as I do not ihink that, as yet, its stability is in any 

 degree problematical, 1 shall endeavour to show on what mv 

 opinion is founded. Prof. Green remarks, " 1 have do 



