TO 

 SAMUEL GEORGE MORTON, M. D. 



MK.MHKK OF THE AMERICAN PHILOSOPHICAL SOCIETY, 



CORRESPONDING SECRETARY OF THE ACADEMY OP NATURAL SCIENCES, OK 

 PHILADELPHIA, AC.' 



In 'publishing the fossil shells of our Tertiary formations, it 

 is a pleasure as well as a duty to inscribe to you a work, which, 

 whatever its merits, would not have appeared without your en- 

 couragement and assistance. Your zeal for establishing the 

 geology of our country on its only permanent basis, organic 

 remains, has added a valuable collection of American fossils 

 to the Academy of Natural Sciences, from which I propose to 

 figure and describe the greater number of species contained in 

 the following pages. I sincerely regret that your professional 

 duties are too arduous to permit you to undertake a work for 

 which you are so much better qualified than myself ; for with 

 such ample materials, you could not have failed to render it ac- 

 ceptable both to the geologist and the student in conchology. 



T. A. C. 



