iv PREFACE. 



Again, the scrutiny which is at present directed to the 

 anatomical structure of the animals inhabiting shells, has 

 given rise to the establishment of many new genera, and 

 has tended, more than any other circumstance, to fix the 

 distinctions of this science on a natural and permanent 

 basis. 



It is therefore proposed, in the present work, to adopt, 

 tvith very few exceptions, the genera of Lamarck and 

 Cuvier, together with such others as have been judicious- 

 ly indicated by Sowerby, Blainville, Say &c. 



It is designed to give brief descriptions, and accurate 

 figures, of all the shells inhabiting the Atlantic coast of 

 North America, and to publish them in monographs, each 

 of which will embrace all the known species of a genus. 



The great extent of our sea coast would lead us to 

 conjecture, that many shells had hitherto escaped the 

 observation of our Conchologists : such has proved to be 

 the fact, and the author, in mentioning this circumstance, 

 takes occasion to return his sincere thanks to those gen- 

 tlemen, whose hberality has given him access to their 

 collections, and thus rendered them subservient to the 

 cause of science. To the Academy of the Natural 

 Sciences of Philadelphia, he has to acknowledge particu- 

 lar obligations for the unreserved permission which has 

 been granted him to publish the nondescript species in 

 the collection of that institution. 



In the descriptions of the bivalves I have followed 

 some distinguished Conchologists in terming the distance 

 between the anterior and posterior extremities of the 

 shells, their length ; the height is from the opposite, or 

 basal margin to the beak ; and the breadth is the great- 

 est extent between the outer surface of the valves, when 

 closed. I have also adopted Mr. Gray's term cartilage, 

 for the substance which acts like a spring to separate 

 the valves ; and the ligament is that which binds them 

 together at the hinge margin. 



Philadelphia Afril, 1831. 



