PREFACE. 
text and the later plates of this volume the author cheerfully acknowledges the 
very valuable assistance rendered by Mr. Charles E. Beecher. 
Of the mechanical and artistic execution of this work I may speak with 
commendation. Regarding the scientific character of that part of the work 
already published and its value to the general public, we have had the testi¬ 
mony of prominent scientific men; and I hope the present volume may be 
regarded as an acceptable contribution to our knowledge of a class of fossils of 
which little systematic information has heretofore been given. 
The author has been indebted for the use of specimens for study and illus¬ 
tration to Dr. James Knapp, of Louisville, Ky., to E. B. Knapp, Esq., of 
Skaneateles, N. Y., and to Mr. Charles E. Beecher. To the collections of the 
Cornell University he is indebted for two specimens illustrated in the present 
volume, and for several others which are illustrated in the plates already pre¬ 
pared for the next volume. 
JAMES HALL. 
Albany, February, 1884. 
