19 



nob. U. acalu^, Say, Anodonta declim's, nob. To aU 

 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 

 tSrjmvhynota, 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 o{ 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 

 slielis. "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 ochracens, 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 



