x PREFACE. 



texl and the later plates of this volume the author cheerfully acknowledges the 

 very valuable assistance rendered by Mr. Charles E. Beecher. 



Of the mechanical ami 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, L884. 



