26 



OBLIQUE. 



cor. Con. 



truncatus. Swain. 

 *Hanleyianus. Lea. 

 *decisus. Lea. Con. Kiist. Chenu. 



*clavus. Lam. Con. Menke. Kiist. 

 Unio scalenia. 

 Unio modioliformis. Say; not of Lea. 



*patulus. Lea. Con. Desk. Chenu. 



*oviformis. Con. 



*argenteus. Lea. Chenu. 



*Ravenelianus. Lea. 

 Unio rudis. Con. 



*Troschelianus. Lea. 



*strictus. Lea. 



*Rangianus. 1 Lea. Chenu. 



Unio gibbosus. Kiist. (PL 4, Fig. 4.) 



*sulcatus. Lea. Lot. Say. Lesh. 

 Chenu. 



I 



OBLIQUE. 



Unio ridibundus. Say. Lot. (Fe- 

 male.) 2 



*Haysianus. 3 Lea. 



^ellipsis. 4 Lea. Say. Eat. Potier. 

 Chenu. 

 Unio brevialis? Sow. 



*castaneus. Lea. Chenu. 

 *pulvinulus. Lea. 



OVAL. 



*Tampicoensis. Lea. Chenu. 



*Lecontianus. Lea. Chenu. 



Unio contrarius. Con. 



*hebes. Lea. 



*perdix. Lea. 



Unio pectorosus. Con. Kiist. 



*ventricosus. Bar. Adams. Dehay. 

 Unio radiatus. Hild. 

 Lampsilis ventricosa. Stimp. (Agass. 

 MSS.) 



*occidens. 5 Lea. 



1 This species has been supposed by some naturalists to be the same with perplexus (nobis). Mr. Clark, of 

 Cincinnati, informs me that the animal differs in color, being lighter. It is known there vulgarly as the " White 

 Mouth." I think they are certainly distinct species. 



2 For some years, I was satisfied that Mr. Say's ridibundus was only a variety of stdcatus (nobis). There can 

 now, however, scarcely be a doubt that it is the female of that species; but it must be remarked that this serrated 

 shell is visually found smaller than the other; a circumstance common with the females of some other species. Mr. S. 

 describes and figures ridibundus in No. 1 of American Conehohgy, butdoes not insert it in his Synonymy, in No. 6. 



3 I am very much disposed to think that Haysianus will prove to be the female of Sowerbianus (nobis). They 

 differ much in size, but in other characters are much alike. The latter is the larger, and has never, so far as I 

 know, been found with charged oviducts. The former usually has charged oviducts. 



4 Mr. Say, in his American Conehohgy, refigures this, and recognizes my name. Subsequently, in his 

 Synonymy, he makes it a synonyme of triangularis, Raf. Mr. Conrad says it is olivarius, Raf. 



5 This and the preceding shell are so nearly allied, that it is a matter of doubt with me if it would not be 

 preferable to unite them. Dr. Ward thinks they are male and female. Subsequent examination may throw suf- 

 ficient light upon them to decide with certainty. Among Mr. Barnes's varieties of ventricosus, it is evident there 

 are several distinct species. Prof. Kirtland, in Ohio Reports, says it is impossible, with our present knowledge, to 

 draw lines of specific distinction between the group consisting of ovatus, ventricosus, occidens, subovatus, &c. 



