PREFACE. 



by collectors and amateurs, and thus to insure 

 the determination of the species with ease and 

 certainty. 



Most of the shells have been figured from 

 specimens in the collection of the Academy of 

 Natural Sciences, but a few, not readily 

 accessible to me, have been copied from the 

 works of Messrs. Lea and Binney. 



To Dr: Isaac Lea I am much indebted for 

 the use of the original types of some of his spe- 

 cies which had not been previously illustrated, 

 and which I have thus been enabled to figure 

 for the first time. I am also under great obli- 

 gations to Dr. James Lewis, of Mohawk, New 

 York, and others, for valuable assistance. 



The synonymy accompanies the references 

 to the plates. It will be noticed that two sets 

 of numbers are used for paging. Those in 

 brackets are in continuation of Prof. Halde- 

 man's paging. 



Measurements are made in millimetres, 25 

 z= 1 inch. 



George W. Tryon, Jr. 



Hall of the Academy op Natural Sciences, 1 

 March 25th, 1870. j 



