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OBLONG. 



Unio brunneus. Bonhomme. 

 Unio Woolwichii. Morelet. 

 Unio cuneatus. Jacq. 

 Unio Yalentimis. Rossm. 

 Unio Astierianus. Dup. Grat. 

 Unio umbonatus. Bourg. 

 Unio rhomboidens. Moq. 

 My sea ovataf 1 Turt. 

 Mya rhomboidea. Schr. Bourg. 



SUBROTUND. 



*circulus. Lea. Sh. & Eat. Desk. 

 Chenu. Han. 

 Mya rotunda? Wood. 



*lens. 2 Lea. Chenu. Han. 

 Unio depygis. Con. 



*Beacileianus. Lea. 



*Sbowalterii. Lea. 



*unicolor. Lea. 



rubellus. Con. Han. 



f SUBROTUXD. 



Masoni. Con. Kiist. Han. 



*rotundatus. Lam. Han. 



Unio suborbiculata. Lam. Blain. 

 Unio ghbulus? Say. 

 Unio subglobosus. Lea. 



*Cbickasawhensis. Lea. 



*pauperculus. Lea. 



*petrinus. Gould. 



*IIoustonensis. Lea. 



*Paranensis. Lea. D'Orb. Han. 

 Unio Solisiana (junior). D'Orb. 



*pera3formis. Lea. 



*disculus. Lea. 



*bulloides. Lea. 



*funebralis. Lea. 



membranaceus. 4 Mat. Han. 



1 Turton's figure seems to me to be an elongate variety of littoralis, analogous to that which I 

 described, in error, under the name of incurvus. But Forbes and Hanley say that littoralis does not 

 now exist in the waters of Great Britain, and is only found there in the Pliocene formation, in a fossil 

 state. If this be so, then Turton's figure must be erroneously given. 



" I have some doubts whether this should be considered more than a variety of circulus. I am not, 

 however, sure that it is not distinct. 



3 Although Mr. Say had published this shell in the Transylvania Journal, and in his Am. Condhology, 

 he omitted it altogether in his Synonymy. He inserted other species from the vicinity of New Orleans. 



4 1 formerly placed this with the Anodontse, but D'Orbigny, who has seen the shell in its native waters, 

 having placed it among the Uniones, I follow him, never myself having seen the shell. The figure of Dr. 

 Maton (Linn. Trans., vol. x.) is without teeth, and the text says expressly "cardo edentulus." Notwith- 

 standing this, I am inclined to believe that D'Orbigny is right, for the form of the shell is such as I have 

 not seen in the Anodontse. Not knowing what induced M. D'Orbigny to change Dr. Maton's name, I 

 have restored it. 



(Since this note was published, M. D'Orbigny, in his Voy. Am. 3Ier., has come to a different conclu- 

 sion as regards Mytilus membranacea, Mat. He now thinks that my Anodonta lato-marginata is the same 

 with membranacea, but I do not think that Maton's figure can be referred to lato-marginata, even sup- 

 posing the figure of membranacea made by Maton to be from a young specimen. The outline is not the 

 same, membranacea being much more rotund, and the very great difference of solidity must have its 

 influence in our decision; lato-marginata being one of the thickest of the Anodontse. M. D'Orbigny, in 

 Mag. de Zool., 1835, gives Mya membranacea as a sj'nonym to Unio Matoniana, and says the teeth are 

 thin; but he ought to have cited it as Mytilus, as Maton does not give Mya membranacea, but 3Iytilus 

 membranacea. M. D'Orbigny places it now among the Anodonta?, and restores Maton's specific name of 

 membranacea, and considers my lato-marginata as a synonym. It does not appear to me, from the 

 description and figure, that they can be the same.) 



