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nob. U. alatus, Say, Anodonta declivis , nob. To all 
these species the remarks I have made upon the ha- 
bitat of U. glans are equally applicable. 
It will be observed that I have not adopted the genus 
Symphynota , of Lea, not only for the reason given 
in the Monthly American Journal of Geology, edited 
by Mr. Featherstonhaugh, that as the essential cha- 
racter of Symphynota is the testaceous connexion of 
the valves, it must necessarily include some marine 
shells, such as Pinna , Hyalcea , &c. but inasmuch as 
all other bivalves are arranged by the character of 
the hinge, the disposition or absence of teeth, &c. I 
find no good reason for such anomalous grouping of 
shells, without any regard to those characters deem- 
ed essential in all other genera. In several species 
this connexion is so obscure as only to be observed 
in the most perfect specimens, and Mr. Lea has met 
with a specimen of the Unio ochraceus, of Say, 
which will doubtless require very careful nursing 
to enable it to keep its station in the anomalous ranks 
of his genus Symphynota. Unio, Alasmodonta and 
Anodonta can generally be distinguished even by 
external form, and constitute very natural groups, 
closely allied, it is true, but not more so than many 
well established genera of marine bivalves; and yet 
as some species of each of these genera are connate, 
they are forcibly separated from their respective 
