TO MAJOR JOHN LE CONTE, 
My Dear FRIEND: 
Will you permit me in this way to acknowledge my obligations to 
your great kindness and liberality, in furnishing me, during so many years, with nume- 
rous new species of our fluviatile molluscs? The pains you have always taken in 
bringing to light new forms, may readily be understood by looking through this and 
my previous volumes on this interesting subject. I feel grateful for the untiring assi- 
duity you have given to promote my objects, and therefore it is with peculiar pleasure 
that I present you with this volume. 
Truly and 
Faithfully yours, 
ISAAC LEA. 
