PREFACE. 5 
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 
= | inch. 
GEORGE W. Tryon, Jr. 
Hau or THE AcapEmy or NATURAL SCIENCES, 
March 25th, 1870. 
