21 
tending entirely over it, the superior Lglpaad is 
always extremely. thin, has the appearance of being 
fractured, and a part of it worn away. Future 
observation must determine the number of those 
species, which are connate when young, and occur- 
ring in situations where they are least lable to 
injury. If all fresh water bivalves, possessing the 
coalite hinge, are to constitute one genus, upon the 
same principle, we must arrange the analogous 
marine shells ina similar group, and Pinna, Mytilus 
and Hyalea must all have one new and descriptive 
generic appellation, if Mr. Lea will not admit them 
into his genus Symphynota, which name he may 
apply to the marine connate shells, as Metaptera, of 
Rarinesaue, 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 Can- 
rasan aoa 
ae) retion of sand, formed 
for its habitation by the larva ofan insect. There is’ 

