THE FAMILY NAIADES. 



45 



< 



< 



< 



O 



I 



o 



OVAL. 



Alas, radiata. Con. 



calceola.* Lea. 



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



Alas, marginata.t *SV/y. 



Alas, truncata. Con., not of Say. 



OBOVATE. 



Bonellii. Lea. 



Alas. Bonellii. Fer. 



Unio depressa. Pfeif. Mi'ihl. 



Unio compressa. Menke. 



ARCUATE. 



margaritifera. Zea. 



Mya margaritifera. Zm. Knorr. Dill. Desk. 

 Wood. Mat. Monta. Miihl. Retz. 

 Nil. 

 Margaritana fluviatilis. Schum. 



Although in both these shells there is a small cardinal tooth, in all their other 

 characters they so closely resemble the Jlnodontx, that it is a matter of doubt 

 with me as to the propriety of separating them. An examination of the ani- 

 mals when satisfactorily dissected may show the propriety of placing them 

 both, notwithstanding their possessing small teeth, with the J]nodontx. 



* In my Memoir in the Trans. Am. Phil. Soc, Vol. III. page 420, (page 

 34 of " Observations on the Genus Unio,") I mention this shell as being 

 closely allied to the genus Alasmodo7ita 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. 



j" Mr. Say in his " Synonymy" makes calceolus and Jilas. marffinata 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. 



