21 



tending entirely over it, the superior portion is 

 always extremely thin, has the appearance of bein.s- 

 fractured, and a part of it worn awa}-. Future 

 observation must determine the number of those 

 .species, w^liich are connate when young-, and occur- 

 rino* in situations where they are least liable to 

 injury. If ail fresh water bivalves, possessing the 

 coalite hing-e, are to constitute one genus, upon the 

 same principle, we must arrange the analogous 

 inarine shells in a similar group, and Pinna, Mytilus 

 and Hyalcea must all have one new and descriptive 

 generic appellation, if Mr. Lea will not admit them 

 into his genus Symp?iynota, which name he may 

 apply to the marine connate shells, as Metapiera, of 

 IvAFiNEsauE, has priority among the Naiades. 



Amongst the fresh water shells described by Mr. 

 Lea, is the habitation of the larva of an insect, form- 

 ed of a concretion of sand. He gives Cumberland 

 river as the locality of this supposed shell, but it 

 occurs abundantly in Wissahickon creek, where I 

 found specimens more than twelve years since, and 

 it has long been well known to the first Conchologist 

 in the United States, the distinguished Mr. Say, 

 whose profound knowledge of Entomology and Con- 

 cliology would not permit him to regard as a species 

 of VaJvata, a turbinate concretion of sand, formed 

 for its habitation by the larva of an insect. There is 



