22 
another kind of these curious domicils in Wissa- 
hickon creek, so perfectly like a Crepidula, that it 
might with equal propriety be added to the species 
of that genus. Should Mr. Lea obtain this, he may 
erect a new genus to receive it; as fresh water and 
marine shells, according to his theory, cannot with 
propriety be arranged in the same genus. The shell- 
formed receptacle of the Phryganea , called by this 
writer Valvata arenifera, is widely distributed 
throughout the United States. It abounds near Phi- 
ladelphia and in the vicinity of Baltimore, and I have 
found it equally abundant in a creek in South Ala- 
bama. I never mistook it for a shell, not even when 
I collected it, during my solitary rambles in early 
youth, along the wild and romantic banks of the 
Wissahickon, where a passion for the beautiful in 
nature, as well as a taste for natural science, often 
led me on the fine days of autumn and spring. 
It is with pleasure I acknowledge the assistance I 
have received in prosecuting my researches, from the 
kindness and liberality of several gentlemen in Ala- 
bama. I shall ever feel grateful to them for their 
attentions to a stranger, who sought health in the 
bland air of a southern clime, and recreation and in- 
struction in the study of fossiliferous strata, in a 
State, probably the richest of the Union in organic 
remains, and certainly more interesting than any 
