MARGARITANA. 



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OVAL. 



radiata. 1 Lea. 

 Alas, radiata. Con. 

 Uniopsis radiata? Swain. 



*calceola. 2 Lea. Kiril. 



Unio calceolus. Lea, Trans. Am. 



P. S. Desk. Chenu. 

 Alas, marginata. 3 Say. 

 Alas, truncate/,. Con., not of Say. 



WIDE. 



*Hilclrethiana. 4 Lea. 



Unio Hildretluanus. Lea., Trans. 



Am. P. S. 

 Al. ambigua? Say. 



*dehiscens. 5 Lea. 



Unio dehiscens. Say. Desk. 



Unio oriens. Lea, Trans. Am. P. S. 



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OBOVATE. 



*Bonellii. Lea. Villa. 

 Alas. Bonellii. Per. 

 Alas, depressa? Villa. 

 Alas, compressa. Villa. 

 Unio depressa. Pfeif. M'uhl. 

 Unio compressa. Menke. 

 Unio Bonellii. Menke. 



ARCUATE. 



*margaritifera. s Lea. 

 Mya margaritifera. 

 Born. Schrot. 

 Chem. 

 Desk. 

 MuU. 



Lin. Mill. 

 Pennant. Bon. 

 Ba Costa. Bill. 

 Mat. Monta. 

 Schreib. Cuv. 



Knorr. 



Wood. 



Nil. 



Bup. 



crassissima. Klein. 



Margaritana jluviatilis. Schum. 

 Margaritana arcuata. Stimpson 



1 This shell, in the teeth, except in the size of them, very closely resembles the An. areolatus, Swain, which 

 Mr. Say described as Alas, edentula. Although in both these shells there is a small cardinal tooth, in all their 

 other characters they so closely resemble the Anodontee, that it is a matter of doubt with me as to the propriety of 

 separating them from that genus. An examination of the animals, when satisfactorily dissected, may show the 

 necessity of placing them both, notwithstanding their possessing small teeth, with the Anodontee. Swainson, in his 

 Malacology, refers to radiata as his Uniopsis radiata; but this must be an error. 



3 In my Memoir in the Trans. Am. Phil. Soc, vol. iii. p. 420 (p. 34 of "Observations on the G-enus Unio"), 

 I mention this shell as being closely allied to the genus Alasmodonta of Say. In this Synopsis, I have deemed it 

 better to transfer it to the subgenus Margaritana, as the lateral tooth is observable in very few individuals. Deshayes 

 says it is between Unio and Alasmodonta. 



3 Mr. Say, in his Synonymy, makes calceolus and Alas, marginata the same. I am surprised at this, as their 

 characters, in many respects, are very different, and I have never heard it even suggested before that they could be 

 confounded. 



4 In the previous edition, this was placed among the Uniones with much hesitation. I now think it groups 

 better with the Margaritanm. Its cardinal tooth is very much like M. Bonellii, and the callus of the dorsal margin 

 is sometimes, in both, so much thickened as to present an imperfect appearance of a lateral tooth. Mr. Say's descrip- 

 tion of ambigua answers well to Hildrethianus, but I am not sure it is the same, as he has given no figure of it. 

 He seems to have abandoned it, as he does not insert it in his Synonymy. Mr. Conrad also avoids the insertion of 

 it in his Synoptical Table. 



5 Mr. Say, in his Synonymy, gives Mr. Kafinesque's name of lata precedence. Mr. Eaton says that An. lata, 

 Raf., is Symphynota tenuissima, Lea. 



6 Klein describes this species under the name of crassissima, but with no generic term. This name has been, 

 by Ferussac and other zoologists, erroneously applied to the large Unio, common to the south of Europe, which 

 Ketzius described as Unio crassus, and I have given it to Eetzius. Klein's crassissima is the true Margaritana 

 margaritifera {Mya margaritifera, Lin.), and his figure of it, PI. x. Fig. 47, is a copy of Lister's, Tab. 149, Fig. 4. 



